Devs should have in mind that four main characters may scale up the game to an unmanageable size for a small group of developers. I explain:
If the game is intended to fully follow each of the characters possible paths, it would have:
(Assuming each girl would have just one lover option other than dad, and dad would have only one lover option other than his daughters)
Daughter 1- Alone, With Dad, With Another Guy
Daughter 2- Alone, With Dad, With Another Guy
Daughter 3- Alone, With Dad, With Another Gal
Dad - With Daughter 1, With Daughter 2, With Daughter 3, With Another Girl (Plus variations like: With Daughter 1 + Daughter 2, With Daughter 1 + Daughter 3, With Daughter 1 + Another Girl...and so on...)
If their stories are intertwined, for instance:
They all go together to a restaurant, Daughter 1 alone, Daughter 2 with Dad, Daughter 3 with another Gal. The possible scene variations multiply and they multiply even more if the game gives different clothes options.
Maybe fully following only the MC possible paths (with all available girls and their combinations it would be already a lot) and just showing one interactive event involving each daughter and a different lover would keep the game into a feasible size. Otherwise there is a risk of this game never being finished.