Hello TigerKing582,
Welcome to Microsoft Q&A forum.
A purchase is permanently bound to the account that made it, and the entitlement cannot be transferred. So, unfortunately, transferring the game license from your parent's account to your is not possible.
However, there is a workaround for it, that is to use your email as login credentials to your parent account. but there are also some requirements and condition that need to be met.
- Your account email address shouldn't be a Microsoft domain (outlook.com for example).
- When it is done, your parents will also lose the access to their mailbox if they use Outlook, so please backup before we proceed.
If it is okay with you, please let me know.