We just don't get along. My niece is the one who really cares and has been trying to help me. There are only two ways that a child can legally exercise any kind of control over a parent's money. First, the parent can voluntarily give the child power. Second, the child can try to take control by forcing a Guardianship over the parent.
Guardianship is a long, complex legal process.
Your son is actually high on the list of legally preferred helpers. Since you don't want him you'd better take some legal action to lock him out. This allows you to name someone to become your Guardian should you ever need a Guardian in the future. It gives you control over your own future guardianship. To make a Declaration of Guardian you must be competent and you must be over age 18.