What is my probability of getting guardianship of Dad?

Actually, I think you should pursue Guardian status for the wife. Proving she is incompetent would automatically remove her as POA and Executor. That might be a good thing. You don't have to actually be the Guardian, you can let the courts handle her bad behavior. Another good thing.

I agree, pursue guardianship for his wife. The next time she is physically abusive, I think someone needs to call 911 and tell someone that she is a danger to others. Your father should not be subjected to physical and verbal abuse just like any other spouse should not be subjected to such treatment.

Hard to prove she's incompetent... she's 15 yrs younger, there is home health care, abuse is done privately... she can turn on a dime into some sticky sweet thing and convince most everyone that all is well. I think my dad is fearful of rocking any boat with her. she's not related to any of us kids either and has no children of her own.

Wow, that ability to turn into someone sticky sweet on a dime sounds to me just like someone with a personality disorder like borderline. I'm sorry that he is afraid of her.

Well, you can't get the guardianship while Dad is clearly competent, unless he would agree not to challenge it. If he does start to slip, get it before she does. Bad enough she got the POA. See if you have any hard evidence of abuse of the POA financially or otherwise if you can, because bad POAs can be removed by a court, but you will have to be discreet about it. Dad, while competent, could change the POA to you but she would probablly just coerce him into changing it back.