Welcome! Thank you for your question.
Unfortunately the creation or amendment of a revocable living trust does not have to be notarized under Missouri Uniform Trust Code Section 456-006-602. http://www.moga.mo.gov/statutes/C400-499/4560060602.HTM
The grantor (your father) does have to be competent to complete the amendments. Competency is the same requirements as that which is required to make a will under 456-006-601. http://www.moga.mo.gov/statutes/C400-499/4560060601.HTM
The competency required to make a will is 1) knowing the nature and extent of his assets and 2) knowing who his natural heirs are at the time of making the revisions.
To prove that the amendments to the trust are invalid then you will need to prove that your father was incompetent at the time the amendments were made.
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