Have you tried games from NLT Media?
Treasure of Nadia
The Genesis order
I have and they are great too
Dark neighborhood,filf,dreams of desire,Sumer time saga
have played dreams of desire and summertime saga, will try others
Don’t know a lot of incest games (especially with such a long playtime) but I know of Seikatsu – Fantasy.
Appears to have been abandoned, but:
My Sister, My roommate
Daughter for Dessert
Cure My Addiction - Cousins, loop kind of sucks but it is pretty longish.
Big Brother - I can’t in good conscience recommend playing it, but a lot of people love it, it is a slough.
These are listed from top to bottom in my strength of recommendation.