For some of these I used the comics

( You are 15)

Tony:
Morgan Stark (younger sister) and Peter Parker (your adopted slightly younger brother)

Steve:
None

Natasha:
None

Bruce:
None

Clint:
Cooper, Lila, Nathaniel Barton (older siblings)

Pietro:
Luna Maximoff (Older sister)

Wanda:
Thomas and William (older twin brothers)

Loki:
None

Thor:
Trud and Modi (your younger half siblings, the children of Thor and Sif)

Bucky:
None