He's fully aware of people and surroundings and can still drive. My mom is burned out from being accused of spying and taking money. He is fully aware of most things, it is just the paranoia that is driving her crazy.
The hard part is over.
I'm matching you with one of our specialists who will be calling you in the next few minutes.
What meds was tried on your dad? Has he had a geriatric neuropsychological evaluation? As sunny mentioned, if his behaviour gets too difficult he may need to be placed in a facility. This is very difficult for all family members and especially for your mother. (((((hugs)))))
Not only can emotional distress be taxing on family members, it's painful for the person who is suffering as well. That's why would treat it very seriously. This type of behavior can pass, but there is no way to know how long it will last.
If your mom is not able to deal with his behavior, then, I'd explore options. It is very exhausting to care for someone who is constantly making false accusations, displaying paranoid and threatening behavior. Sometimes, the person can not be dealt with in a residential setting. I'd ask for help from his doctor or a psychiatric hospital.