Budgie and cockatiel

One of my budgies is always chasing one of my cockatiel and trying to sit on him. Basically the cockatiel is not cool and is always running away from him but the budgie is never leaving. I understand that it may be mating behaviour but both are male. And just previous week this budgie beat up his dad and almost killed, he like became aggressive out of nowhere. I have no idea what to do please help