Think about this. What if you can fuck up your dad even more (that is if you've fucked him up over for the twins)? Celia has asked your help to uncover her blackmailer. Either she's too smart and has caught on to you, or she's too dumb and legit needs your help. If it's the latter, what if you can frame your dad? XD
They are all supposed to be dumb, otherwise how would MC got to manipulate all of them. Except twins, they are relatively smart. I underline relatively because MC is retarded, so outsmarting him is not big thing. He is ruining his future for one shag, when he can have up to four shags daily with higher value girls. It also makes Celia, mom and sisters on eve lower level than MC.
Yeah, yeah I know the vibrator in the class scene would be impossible for dad to do, but maybe you can act naive and tell that your dad forced you to use it and you didn't know what it was and what it would do, then poor dad is out of the way for us!
I think MC can manipulate some girl into dominating dad on regular basis, and leaving rest of family to him. There is sadistic neighbour. But it would require MC growing some brains fast.