How do I delete a child's icloud account?

Hi Everyone,

I'm hoping someone can assist. I have had 2 ipads set up for my daughter in the past, they are no longer in use, and I wish to remove them from the family sharing. However these said Ipads have had their passwords and phone numbers changed by my Ex and I can no longer access icloud with them to remove them. I am also at the maximum for family sharing.

How do I set up the new Ipad and link it to the family sharing? Is there a way to delete the old ID's?

Thanks in advance