You could still justify it in the Friend path. On one hand (if you go the friend route but plan to stab Eric in the back) Eric just uses Max to prove he's a good guy, but Max still has too much sway with his sisters so he can't just get rid of him afterwards. So as long as Max remains on the good side of his sisters, he's in the clear. And on the other hand (if you plan to double team the family with Eric), Alice, Lisa and Ann aren't going to do the nasty with you if they don't like you. Just remember that Eric's influence isn't a seperate entity, but a slider. The more influence he has, the less you have (but the more you have, well, he still has influence since that's story driven).
It's just a game over mechanic that forces you to spend time with your family, making it actually a non-issue. If you spend the entire time in your room, just skipping time and not doing anything, it'll lead to a game over (and why would you even do that?), but if you play the game, you won't even notice Eric's influence.