As far as challenging the trust, there is a good chance the statute of limitation has run on that. That said, financial elder abuse statute is four years. That might be explored. While I really dont like to advocate malpractice actions, you may also have to consider that option if the facts are as good as you say in your favor.
Regardless, you need to act to protect your rights no matter what that means you need to do. Dont sit back and wait for time to run.
The general advice above does not constitute an attorney-client relationship: you haven't hired me or my firm or given me confidential information by posting on this public forum, and my answer on this public forum does not constitute attorney-client advice. IRS Circular 230 Disclosure: In order to comply with requirements imposed by the Internal Revenue Service, we inform you that any U.S. tax advice contained in this communication (including any attachments) is not intended to be used, and cannot be used, for the purpose of (i) avoiding penalties under the Internal Revenue Code or (ii) promoting, marketing, or recommending to another party any transaction or matter addressed herein. While I am licensed to practice in New York and California, I do not actively practice in New York. Regardless, nothing said should be deemed an opinion of law of any state. All readers need to do their own research or pay an attorney for a legal opinion if one is necessary or desired.
Find an attorney experienced in these matters and request a consultation. Second opinions can be valuable.
As an aside I have never seen an undue influence case litigated successfully without engaging experts like a forensic psychiatrist.