Control.
It's all Dad want's. He'll do anything to have control over everything he can. He doesn't give two shits whether or not his obsessive behaviour is tearing this family apart, and ruining David's relationship with his girlfriend.
Whenever someone dares to challenge him and to back the hell off for once, he'll go into a rage and accuse everyone of knowing nothing, and that everything will fall apart with him. Amazing that he doesn't realise the irony in that.
Poor Mum is losing her one chance at her psychology qualification for her dream job, David's friendships are being destroyed (alongside his relationship) and Chris is struggling to deal with the stress all because Dad can't come to the realisation that he is not the perfect being he seems to think he is. He's an arrogant prick.