how to tell my dad he needs therapy

My dad is emotionally retarded i don't know what other way to put it i only found out a few days ago from my mom that his dad was abusive and its what he grew up with, i get he doesn't realize when he gets really angry but it is emotionally draining to me and my brothers, if i tell him he should go i will get in trouble so i do not know what to do, my mom has said it to him multiple times and he has never gone because he doesn't realize he has a problem.