I'm currently looking into this, i will try to make an incest patch for this game.
Btw i had to pay rent at home when i started working, i believe it's normal to pay for your upkeep when you still live at home.
At first glance it's going to be mom -> her daughters -> sisters
to mc it will be -> his aunt and cousins
If i'm going to make this work it will be an estranged family, probably on the mothers side because she died at shildbirth.
edit: Or i can take the easy way and just make Lucy a cousin