I purchased a property 15 years ago as a joint tenant with my partner. My mom also made a financial contribution . However, we lack formal documentation to verify her contribution, aside from a handwritten agreement between us that specifies the amount and states she would only seek repayment if the property were sold. In the last 15 years he has changed and been dishonest multiple times, I would like to protect my mom's share. Is it possible to create a formal document to address this situation now, or would it just be no use.