Given the implication that MCs dad was fucking his sister, one twist could be that MC is his aunt's son. Of course, that doesn't explain the red hair genes for Lily
The details in this game are confusing as hell. For example, I'm not playing with any patch. But the game states earlier that Tulip and MC are twins. Then later, Bea tells them they aren't at the funeral. And because of this, the details are getting lost.
The dad's mistress states that Lilly being a redhead sort of denies Andi of being his mistress. Since she thinks the redhead gen doesn't come from him. However, before that scene, Bea states that when MC was dating Gail. They asked if MC's dad had redhead relatives. Since there's not that many redheads in the county and they thought maybe Gail was related to MC's dad side or his mother side. Which would imply that the dad has some level of the redhead gen in his family. But at the same time, they didn't find any.
Either way, I think the dev didn't really research the whole puberty thing, or is ignoring it because it's fiction. Like most shotacon hentai out there. Otherwise, the timeline implies it's more towards MC than the dad. Unless she was fucking both of them for some reason. She's a pedo though. And so was the dad. Since he married Selena when she was 13 and was doing some wild shit with his sister, who I'm guessing is younger than him.
Lilly is 18. The event happened 19 years ago. MC was raped by Andi when he was 8. Which puts the events extremely close together. Since it takes up to 10 months to give birth and then another year for a baby to turn 1. Meaning, the window is too small for anyone else to be considered. And since Andi was obsessed with MC and on the run after it, I doubt she had time to have sex with someone else. Or that she even wanted to.