You should consult with an Estates and Trust attorney. You may have a claim for waste and mismanagement premised on a theory of negligence. Whether you have sufficient facts to plead and sustain a claim of intentional waste is very fact sensitive and would also be considered by the attorney you consult with on the negliegence claim. You must address this with an attorney immediately as the deadline or statute of limitations for claims of intentional misconduct is one year from the date of wrongdoing.
It's the rare occasion that a broker acts as a guardian or POA for a client's account, given the inherent conflicts of interest. If this individual was acting in the capacity you say they were, then their broker/dealer was required to have notice of that and supervise him accordingly. Now that doesn't mean that just because you lost money you have a case. When you say "self-managed," that term could mean many things in the context of a guardianship. In any event, be aware that if you're looking for recourse from your broker, you will have to arbitrate before FINRA. There are time limitations that apply to such proceedings, so please consult with an attorney immediately to fully discuss your fact situation and review your documents.
The foregoing is not legal advice nor is it in any manner whatsoever meant to create or impute an attorney/client relationship.