People are going to recommend specialist or convincing them to get hearing aids and what not but that's just not it.

Growing up, my grandad lived with us. And he's exactly as you describe your parents. Deaf and stubborn but refusing hearing aids. Having temper tantrums, etc.

The way to deal with it is honestly to be firm and to set hard boundaries. But at the same time you've got to be able to redirect them and sort of distract them by allowing tolerable BS so as to avoid really destructive bs old people can do.

For example, my parents would indulge my grandfather in his doctor shopping medical bullshit. They'd let him go to different doctors about his diabetes and general age related illnesses and change meds. Inconvenient to take him to clinics and fill his ever changing prescriptions but better than him constantly bitching about his partly imagined health issues to us and to the rest of the family and doing his oh misery is me, nobody cares for me bullshit. We could always deflect by saying you just went to the doctor last month or last week.

We wouldn't let him drive at all. When we moved him in with us we made sure to have his vehicle left at his house in the ghetto. Not driving was a hard boundary. My grandad was prone to getting confused, had poor eyesight and was hard of hearing. So when he'd demand to get his car or want to go off somewhere on his own, we'd always deflect. We'd offer to drive him or offer to do whatever bs menial errand he'd decided was massively important. However, you have to make sure it's at your own convenience. You can let them take over your life like that.

When he'd get upset at something or other like politics, you've got to listen and let it go in one ear and out the other. You can't let your emotions outwardly match theirs. The same way a parent would grit their teeth and flatly respond to a 6-year old child's bullshit, you got to deal with the elderly. You cant be screaming, if they are screaming, it just escalates. You listen, you don't take it personally, and you deflect from that topic as quickly as possible. You tell them, you'll look into it, you'll try. Maybe later. Maybe next week. Oftentimes they'll forget that shit anyways.

Oh and finally, make sure they don't hold any actionable power over you. Like financial power or ownership of the car or house that you use or live in. An old person can be very vindictive and will use it to abuse you if they can. For example, my grandad, had a bunch of money sitting in the bank on account of being a massive miser and offered it to my parents when they were buying a house and stuff. They never took it. My aunt did and still regrets it. He was real mean to her about that loan. It's just not a good time.