I am going to prove Squall, Ellone, and Rinoa are all from different families!

Squall- Laguna and Raine: Moombas of Disk 2 call Squall 'Laguna' because they share blood and Ellone's statement of Raine dying before she showed Laguna her baby boy who went to an orphanage.

Ellone- ?: Beginning of Disk 2. Laguna: "Dear Ellone's parents, Ellone was a good girl today."

Rinoa- Gen. Caraway and Julia: Beginning of Disk 2, ask Kiros about Julia. He says that she married Gen. Caraway whom Rinoa earlier revealed as her father and whom later 'pulls some strings to get her out' of the Desert Prison.

Ellone X Squall- Squall says " We weren't related. We all just called her Sis because she was the oldest."

Squall X Rinoa- No common parent.

Ellone X Rinoa- No common parent.