We are unable to move our son from one family account to another

Hello, my husband made my son a member of his family account some years ago. We would like to create a new family account under my name so that I can control my son's screen time. We have been completely unable to navigate this. Help! My son is 13. He is unable to accept my invitation to join my family because it says he is already a member of another family. But my husband is unable to remove my son from his family, and he also has never received a request from me by email or text, even though the instructions say he should. What are we doing wrong? I have an iphone, my son has an iphone, my husband does not have an iphone but he does have a macbook. We are desperate to limit my son's screen time as the ap we are currently using to do that -- qustodio, is no longer effective because my son is able to logon as a parent and adjust the settings! Thank you!