(Song that I think REALLY fit will be in bold)

Sydney:

-Washing Machine Heart - Mistski
-Die in a Fire - The Living Tombstone
-It's Been So Long - The Living Tombstone
-Mystery Meat - Sodikken
-Blow My Brains Out - Tickle Me
-Body - Mother Mother
-Lotta True Crime - Penelope Scott
-Whats Gonna Happen - Sarah Stiles
-What If Things Get Worse - Kaden Macnay
-Our Word - 36 Questions
-Fall Fair Suite - Ride The Cyclone Musical
-Bruno is Orange - Hop Along, Queen Ansleis, Frances Quinlan
-Are You Satisfied? - MARINA
-Oh no! - MARINA

Li'l Sydney:

-Make Believe - Jakeneutron (King)

(That's kinda all I got at the moment but I'll update if I find more. Feel free to suggest some!!)

Petey:

-Make Believe - Jakeneatron (Collector)
-Your Imaginary Friend - Lemon Demon
-Lights On - Kyle Allen Music

Peter:
(Oh boy, there's a lot..)

-Problems - Mother Mother
-Has Anybody Seen My Will To Live? - The Tin Knees
-Fearless Hero (Hero Version) - Puss In Boots: The Last Wish
-Feel Better - Penelope Scott
-I Deserve to Bleed - Sushi Soucy
-The Main Character - Will Wood
-Amnesia Was Her Name - Lemon Demon
-Ghosts - Jacob Tillberg
-Sex Sells - Lovejoy
-It's Over Isn't It - Steven Universe, Deedee Magno Hall
-Riptide - Vance Joy
-She Wants Me (To Be Loved) - The Happy Fits
-I / Me / Myself - Will Wood
-Twin Size Mattress - The Front Bottoms
-Lone Star - The Front Bottoms
-Turn the Lights Off - Tally Hall
-Touch-Tone Telephone- Lemon Demon
-Foundations - Kate Nash