You are not going to have a "Come to Jesus" with him that will do any good in the long term, as what you are seeing is a decline in metal health.
Ask yourself this:
Does your dad lack the capacity to make informed decisions about his own medical treatment?
Is he able to, on his own, provide for himself? Is he "Gravely Disabled"?
Gravely disabled” means the person is unable to provide(on his own) for basic personal needs (food, clothing, shelter) or lacks insight into the need for treatment and unwillingness to comply with treatment that is likely to lead to an inability to provide for basic needs.
Would he be considered mentally ill?
Mentally ill” for example means a person, who as a result of a substantial disorder of thought, mood, memory, (perception of reality from watching nothing but Fox news, thinking that is 100% reality) etc, etc, which grossly impairs his judgment, behavior (wild behavioral swings), capacity to recognize and adapt to reality, requires care and treatment at a facility.
If this sounds accurate, then your father is mentally ill and at the very least needs to have a mental health evaluation. He of course will be on his best behavior, but if you have a private meeting beforehand with proof and examples of what he does, that will go a long ways towards giving a proper total picture to the mental health examiner so they can make an informed decision that is best for both your dad, and your mom.
Start writing stuff down in a behavior journal. It will be important.
Honestly it sounds like he has onset of dementia, and it is time for him to be treated. Your mom should not have to be stuck in an abusive hell. If he is being that abusive in front of his kids, what sort of behavioral outbursts are happening when you are not present.
Protect your mom, for both of their sakes.
