About the siding with the mom thing, I don't think anyone will dispute the fact that she's an abusive nut who should face some consequences as well but let's be honest for a sec, who the hell would want their teenage daughter to hang out with a middle aged man?
Siding with the dad is just as weird, he's an adult having a relationship with a 16yo
Reminder that there's no good side in this manga, just fucked up people everywhere