You are right, this is super hard; I had to think about this for a long time.
On the parents thing, I didn't pick a "couple," I picked who I'd want for a mom, and who I'd want for a Dad (that may be what OP was thinking, although Mary Poppins & Jack are an interesting combo).
Kids were super easy - I don't even have / want kids and I would take these two in a heartbeat. Spouse took forever because a lot of the characters I "like"
I would not actually want to be in a relationship with. My final choice kind of came out of left field and surprised me. Oh, and some choices aren't human, but, hey, it's about the personalities.
Parents: James P Sullivan / Frannie Robinson
Grandparents: Maurice / Mrs Potts (animated BATB).
Spouse: Barley Lightfoot
Brother / Sister: Flik (Bug's Life) / Anna
Kids: Russell and Boo
Pet: Dug!