The person drafting the trust needs to be an attorney or he likely violates the rules against the unauthorized practice of law.
If the person is an attorney, then the legal issue is whether he violated the rules of professional conduct in that state. Under the ABA model rules and the rules that apply in most states, a lawyer may draft a will or trust for a family member without it being a prohibited conflict of interest. See Rule 1.8(c) of the ABA model rules of professional conduct, which states "A lawyer shall not solicit any substantial gift from a client,
including a testamentary gift, or prepare on behalf of a client an
instrument giving the lawyer or a person related to the lawyer any
substantial gift unless the lawyer or other recipient of the gift is
related to the client. For purposes of this paragraph, related persons
include a spouse, child, grandchild, parent, grandparent or other
relative or individual with whom the lawyer or the client maintains a
close, familial relationship." Of course, what matters is the law of the state in which this took place, and its rules might be different.
If the trustee breaches his fiduciary duty in managing the trust, the other interested persons can seek to remove him as trustee.