I'll give you J-sama, but I'm pretty sure that
1) prison for Q
2) even if J-sama is a glaring plothole, the delusion that this porn star "can't be my sister" is a pretty strong driving force.
It's especially glaring because he has lived there for YEARS at this point, and 2 older sisters never came up in conversation or existed in pictures in the house? Seriously? Holidays, Birthdays, nothing? How about visiting Quinn in prison? Was she in solitary the whole time?
The whole meeting the sisters thing would have worked if this was like a year after he moved into the house, but exactly how old were these sisters exactly that they weren't there when he was growing up? He's 21, Julia is younger by what appears to be a few years (she's in college we know that), and we can guess how long he's been in the house based on Quinn. She was in prison for 8 years, so he was at the very least 13 in the opening, though he looked more like 11.
So 8 years at least where the 2 other sisters never (couldn't) visit, call, or have any kind of interaction with their younger brother, sister or mother.
I'm sorry Dev, but this story is so full of plot holes, it's pathetic.