Please help me with this family situation?

Yeah, here's the rub. You CANNOT be a friend and parent. Children, which they are, MUST be protected and sometimes that means protecting from themselves. First, you need not apologize you need to climb all over them even harder for being manipulative and for ignoring your orders to cool it. We don't care whether what they are doing is "normal" or not. What we do care about is that they need to be protected and by jingo, you must do the protecting. Take the dad gummed PDA away.