I love how people try to read between the lines and pretty much fail but think they're assumptions are facts regardless x_x

cloud then says "i guess that only works with real families." thats means that they live together but arent married and have 2 adopted children.
Ever have friends you consider family? That statement doesn't necissarily mean they adopted anyone. I'm not sure adoption even exists in FF7. Barret took Marlene in as his own, and calls her his. So emotionally he's adopted her. And Cloud and Tifa care about her. That doesn't mean they've taken custody of her. They're taking care of her. And Denzel. And probably any other kid they happen across that they can. I'm pretty sure the whole theme was a lot of parents were killed by the asteroid so there was a lot of homeless orphans running about.