all of them are false except for laguna and raine being squall's parents

Here: Laguna and Raine are married at some point (it shows laguna's memory of this at the ending) 17 years ago laguna goes off to esthar while raine dies giving birth to their son (note that squall is 17) laguna stays in esthar as president probably unaware that raine had been pregnant.

On the ragnarok laguna says "i've got a lot to say to you" or something like that, Kiros says "you look alot like your mother" and ward says (kiros translates) "good thing you don't look like your father" obviously a joke.
so...it makes perfect sense and i guess that would make ellone his foster sister.