Is there a way to hold executors of an estate/fiduciaries to the written law?

The heir, a son, is emotionally unstable. The fear is that anyone with a title higher than Accountant will institutionalize the son to get at the funds for selfish purposes after his mother is deceased. This writer (though this one is not my case) has experienced quite the opposite of what Trust means, and been told by attorneys that any judge will go along with whatever a fiduciary wants to charge; carte blanche (as tho' it was her estate when she walked through the door and declared incompetancy of the mother without a signature).