At the very beginning of the game, we have this monologue from the MC:
"You were excited at first, when you and your sister Haley found entry jobs at the same company. And living together will certainly reduce the cost of moving to the city. But you had forgotten how she can be."
That is followed by:
"The ride over here reminded you... Spoiled brat. Daddy's girl. She's your twin, and only two hours older than you. And to her, that's enough to always break your balls. But she's always been there for you. So, how much can you really complain. How her boyfriend Jack puts up with her, you'll never know. Maybe he's happy that they're now having a long distance relationship."
I don't know where the MC was living, but it doesn't seem like it was with Haley. It also seems like she was living with Jack.
Besides, from their first trip home, which was only a few weeks after they moved in together, they were stunned that the MC's room had been left the same, but everything had been moved out of Haley's.
Also, while they were walking around the house, Haley said, "It feels smaller somehow. The whole house.", which is a comment that would only be made by someone who hadn't been home for awhile.
I can't see any way that they had lived together in their parents house just before moving to the city. The probability is that neither of them had lived at home since they left for college.