Why have more of her family? She just needs to leave the nest on all playthroughs. And all of the characters families are rather distant (we still haven't seen Ian's mom), though Lena's situation has the most involvement, and it's the most boring part of the game (imo). The main reason it's there is to be a money sink, a nexus for drama, and leverage for Seymour.
Ian lives in an apartment with his buddy Perry.
Lena has 2 room mates Stan & Louise.
Both of them have already "Left the nest." They are independent adults, and Lena is even supporting her parents financially.
Is Holly the same? No...
Holly still lives at home with Mom & Dad!
Holly is literally currently grounded because her parents found her birth control pills!
"Leaving the nest" won't be so simply for Holly, or else she would have done it by now.
I understand how you can think having the characters parents be a part of the story is boring, but I think that it adds depth to the characters when done correctly and in moderation.
We have seen many days in the life of Ian.
We have seen many days in the life of Lena.
We have seen 0 days in the life of Holly. 0... Not one. At least not her normal day to day life. Yes, we get her away on vacation for a couple of days at the beach, or for the writing thing when you first sleep with her as Ian. But those are not normal day to day days for Holly. Those are "Holly on vacation" or "Holly on a work trip".
Does her mother still do the laundry for Holly? We don't know.
How did they find the birth control pills? We don't know.
Do they sit around the table for breakfast / dinner as a family still? We don't know.
Does Holly spend all her time alone in her room isolated? We don't know
What does Holly's room look like is it clean or dirty? We don't know.
How often does Holly get "Grounded"? We don't know.
How many Elephants are in Holly's room? We don't know. We know she likes them, but how much does she like them.