My mom now in assisted living was pretty much the same way you mention your dad being, she would rant and get mad at my two sisters and call them names, refuse to do stuff etc.
But when I was there she'd cooperate and do as asked. For example giving up driving, she's nearly blind and had no business driving. Sisters got after her and met the brick wall.
I went over and told her I didn't think it was a good idea to drive any more, dangerous for her and others. No fight, no issue, ok, I won't drive any more.
She was in a nursing home for a month, I visited several times a week even though it was an hour away close to my sisters.
Staff said nothing but fights and no cooperation with sisters but fine when I was there.
I think the trick is to talk with and converse with them, don't insist, be bossy etc. She was dealing with dementia for awhile they think brought on by infections due to improper hygiene living by herself far too long, mostly because I didn't insist she get help, trying to abide by her wishes. Funny thing is she'd be out to lunch but came out of it whenever I was there.
I'm sure all cases are different but I know my sisters approach only made things worse.
In Memory of Paul "Dietrich" Stines.
Dad: Say something nice to your cousin Shirley
Dietrich: For a fat girl you sure don't sweat much.
Cue sound of Head slap.
RIP Muggsy & TMan
"If you are a warrior legally authorized to carry a weapon and you step outside without that weapon, then you become a sheep, pretending that JOCKO will not come today."