So I am just going to give you some info on how I am going to combine these fandoms. Now bear with me cause this took a good while to figure out and a lot of patience. But for now, I will give only up to 4 generations cause it gets complicated even then.
This of course is Sally's side of Persephone's family tree and it is even more complicated and worse as Poseidon's side (.... I think). I am warning you now that I used a lot of fandoms for this!!! Also there will be alot of aus and ocs in this so; if you don't like it then don't read it, but if you still read it then keep your rude comments to yourself.
Plus this took forever to write all this so be happy.

Also I plan on making an story like this one but where it based in Westeros and medieval like.

By the way, the app I use for most of my fictional family trees especially for my fanfics, is called Quick Family Tree. You don't have to sign up for anything and it's free. (( this is not an ad))

So here it is:
Alexander William Jackson was the son of Elizabeth Odessa Shafiq,Tom Marvelo Riddle (Biological father; doesn't know he existed) and Xavier Richard Jackson. Younger Stepbrother to Charoletta Jackson. He will then get married to a Marie Swan. They will have three children together: Lyrria, Richard and James. More on them later. Alexander will died of a Heart attack after learning on James and his wife's demise.
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Marie Josephine Swan is the oldest daughter and child of Matthias Swan and Elyria Madrigal. Oldest sibling to Garrett and Rosemary Swan. Marie got married to Alexander Jackson and they had three children together. She will outlive her husband and her children.
~Garrett Robert Swan married Catherine Iris Tullison and had two children: Charlie and Madeline Swan.
Due to his wife being horrible to his daughter, Maddie, she was sent to live with his wife's distant relatives in Arkansas. (Catherine didn't like Marie so their families didn't interact often) Garrett and Catherine will die two years apart with Catherine dying first due to kidney failure due to her excessive drinking.
- / Charlie Oscar Swan would then get married to Renee Higginbottom and have a daughter named Isabella Marie Swan; they would then get a divorce soon afterwards. They will both get remarried.
— /Isabella Swan would get married to Edward Anthony Masen Cullen and have a daughter named Renesmee Carlie Cullen.
- / Madeline Abigail Swan- would the get married to Jackson Adam Fenton and have three children: Jasmine, Daniel and Danella Fenton.
— / Jasmine Andrea Fenton is engaged to Gideon Martin. Jasmine is a psychologist who specializes with traumatized children. She goes by Jazz.
— / Daniel James Fenton is married to Samantha Ida Manson for almost 4 years and they had twin daughters named Monica Rose and Calypso Serene Fenton (3). Daniel or Danny is working with his parents at the moment part time as well being the ghost king and superhero.
— / Danella Juliet Fenton is dating Xavier Masen Masters. (Currently is 19 and is starting college soon)
~ Rosemary Beverly Swan married Charles Robert Evans and they had three daughters named Petunia, Marigold and Lily Evans.
- / Petunia Anne Evans married Vernon Arnold Dursley and had two children named Heather and Dudley Dursley but Heather would be stillborn unfortunately.
— / Dudley Vernon Dursley married Aubrey Elizabeth Oakens and they have four children named: Thomas, Gwen, David and Juliet Dursley. ( 12,9,7 and 3)
- / Marigold Olivia Evans married John William Grayson and had a son named Richard John Grayson. Marigold or Mary would die along with her husband and few others in a circus accident.
— / Richard John Grayson or Dick Grayson would be adopted by Bruce Wayne after the death of the majority of his father's family and then over the years have numerous siblings. Dick Grayson would married Kori Anders or Kori'ndar who is the Princess of Tameria (?). They would have two children named Mar'i and Jakob Grayson. Dick works with the police during the day and night. (Nightwing).
-/ Lily Margaret Evans married James Fleamount Potter and had a son named Harry James Potter. They would unfortunately die when their son was a year old on Halloween due to unexpectedly and unknowingly to a distant relative, Lord Voldemort. Her and her husband were wand wielding wizard and witch respectively. Lily was a muggleborn and James was a pure blood.
— / Harry James Potter would become an orphan at young age and then taken in by his Aunt and Uncle. But at age 5, he will be taken in by his distant cousin, Sally Jackson. He will then meet
                               : Now to Marie's side :
~ Marie Josephine Swan married Alexander William Jackson and had three children named Lyrria, Richard and James Jackson.

- / Lyrria Penelope Jackson's situation is where it complicated even more so. When she was eight years old, she was sent by an unknown force to another world called  Westeros, there she will be found at the Twins by the Karstarks and taken in by a vassal house and raised there. Eventually she will get to meet and get betrothed to the heir of House Stark at the time; Rickard Stark. They would get married when they are of age (16,19) and had four children named Brandon, Eddard, Lyanna and Benjen Stark.
Eddard (or Ned) and Lyanna would be twins. Sadly Lyrria would die a week later after giving birth to Benjen due to childbirth fever. She was the oldest of her siblings by six years (Richard) and eleven years (James). She was technically the first one to die in her immediate family.
— / Brandon Stark was betrothed but would be killed by the mad king alongside his father during Robert's rebellion. He won't have an legitimate heir but he has a bastard daughter with a merchant's daughter named Aryela.
— / Eddard Stark (Ned) would married Catelyn Tully and have five children named Robb, Sansa, Arya, Bran and Rickon Stark. Ned apparently had a bastard named Jon Snow, it is "unknown" who the mother is. He is the oldest twin brother to Lyanna and becomes the Lord of Winterfell after his father and brother died.
— / Lyanna Stark was to marry Robert Baratheon but she married in secret both Rheagar Targaryen and Elia Martell. She was the stepmother to Rhaenys (?) and Aegon Targaryen, but it is unknown if they are alive or not due to Robert's Rebellion. She gave birth to a son who was named Jaeherys (?) Targaryen but was later renamed by her older twin brother, Jon Snow in order to protect him from those who wished to use or kill him. She died at Childbirth due to bleeding.
— / Benjen Stark is unmarried and isn't able to get married due to taking the black.

- / Richard Elliot Jackson was married to a woman named Octavia Temple for five years and in those years, they had three daughters, but Richard and Octavia got a divorce and Octavia left him with their oldest daughter. Octavia was two months pregnant at the time with the youngest two. Their names were Claudia, Colleen and Connie. Claudia would have the last name Gajos due to Octavia being adopted. Richard would die of cancer when his niece, Sally was 17 almost 18 years old.
— / Claudia Marie Gajos married Noah Stilinski and had a son named Meiczyslaw Stilinski or Stiles but sadly Claudia would pass away suffering from frontotemporal dementia and her son would be with her at the time of her death.
— / Colleen Alexandria Temple married Samuel Holt and had two children named Matthew and Katie Holt.
—- / Matthew Holt
—-/ Katie Holt or Pidge Gunderson
— / Connie Willow Temple would first get married to an abusive man named Teegan Smith but at the same time have a relationship with someone else. She would have a set of twin boys named Samuel and Caine. Both her first husband and lover would die at the same time due a meteorite crashing into the place that they worked. She will give Caine up for adoption but keep Sam. She would get married again but they will get a divorce.
—- / Caine Soren will have a daughter named Gaia with Diane Ladris (can read people's power levels). Caine would have level 4 telekinesis apparently from what Diane saw.
—— / Gaia Soren-Ladris will have empathic power empowerment.
— - / Samuel Temple or Sam will be engaged to Astrid Ellison. Sam would have a level 4 power that would revolve around light that go from a harmless little ball of light to a powerful laser.

- / James Alexander Jackson would get married to a Estella Pevensie and they would have three daughters named Judith, Barbara and Salivera Jackson. They would however, die in a plane crash 1500 miles away from Lake Ontario at 3 a.m after going to visit his parents but left early due to a fight between James,Alexander and Richard. Judith (was 19 at the time), Barbara ( was 15 at the time) and Sally (was 8 at the time) would be raised by their uncle Richard until they live by themselves which wasn't very long in Judith's case.

— / Judith Eloise Jackson or Judy would get married to Ronald Witwicky at age 20 and then would have three kids named Samuel, Carson and Pearl Witwicky. Judith was a 5th grade teacher before she retired when Carson was 10 years old.
—- / Samuel James Witwicky or Sam would get married to Carly Spencer (27)
—-/ Carson Hannah Rose Witwicky (17)
—-/ Pearl Elizabeth Witwicky (12)

— /Barbara Abigail Jackson or Barb would get married to her first husband, James Lake and have a son named James Lake jr. or Jim as he is known as to everyone else. Her husband would leave her for someone else. Barbara is a doctor at Arcadia Oaks Memorial Hospital.  She would get remarried to a man named Walter Strickler (who is a changeling in disguise as the principal of Arcadia Oaks high school) when Jim was 15 years old. She left Sally with their uncle when she was 18 years old cause she had medical school across the country.
— -/ James Arthur Lake jr. is currently engaged to Claire Nuñez. Jim is known as the Trollhunter.

— / Salivera Elizabeth Pearl Jackson or Sally would date a man named Poseidon (who is really the Greek god of the seas) and ended up pregnant with her first child, a daughter named Persephone Jackson. She would get married to a man named Gabriel Ugliano or as he is knowned as Smelly Gabe due to his horrendous smell by Percy. But Gabe was cheating on her with three different women and one of them had a daughter by the name of Lila Rossi. She would turn him to stone with the help of Medusa's head that her daughter, Percy sent her while on a quest. She would eventually meet and married a man named Paul Blofis. They had a daughter named Estelle but they also adopted Percy's paternal half brother, Tyson.
—-/ Persephone Amphitrite Jackson
—-/ Tyson Theseus Blofis
—-/ Estelle Victoria Blofis

Next part would be Sally's maternal paternal side.