What constitutes incompetency?
My mother is physically able to to care for herself on a day to day basis. She can fix meals and still drives, but makes decisions that put herself in danger. My youngest brother is a drug addict & alcholic and has served prison time for DUI. He has had at least three automobile accidents in which the vehicles were totalled, but luckily no one else was hurt. Even though he is on probation, he continues to drink and my mother denies that he is intoxicated. He becomes violent and has regular blackouts. He has made obscene phone calles to other members of the family and we have had to cancel credit cards & cell phone contracts because he makes phone calls to porn sites and charges them to my Mom's credit card. He needs serious help or to be in jail, but my Mom denies that he is responsible and bails him out. I have POA and pay her bills because he lives with her and we are trying to keep information away from him. However, I live 330 miles away and it is difficult to keeps tabs on the situation, especially because Mom lies to protect him. The ideal solution is to get him out of her house, but he does not have a job and she does not want him on the streets. Is it possible to have her declared incompetent even though she can care for herself?
You want to know what "incompetency" is? As far as I know, there is no single, clear-cut, legal definition. "Incompetency" is generally considered to be a question of fact.
The fact that your mom makes decisions that put herself in danger does not, to me, seem to mean that she is incompetent. If she were placing herself is serious physical danger, that could be considered incompetency. But from what you've told me, your mother's decisions involve denial about her youngest son, and bailing him out. That can be foolish or reckless, but that alone does not establish incompetence. If making foolish or reckless decisions established incompetency, millions of American would be incompetent.
If you could prove that your brother's behavior was jeopardizing your mother's finances, risking putting her at risk of grave money problems, that might be grounds to establish incompetence.
You do have a serious and difficult problem. I agree that the ideal situation would be to get your brother out of the house. Unfortunately, your mother's refusal to see the reality you see about your brother means that this ideal situation is unlikely to happen.
Have you thought of talking to your brother's probation officer? Is your brother's drinking a violation of his probation? If so, would you want your brother to be sent back to jail? How would your mother respond to that?
I wish I could give you a more helpful answer.