Re: "Why is it so complicated to remove someone as a member form my family sharing account?"
Wondering if you are the organiser who set up the family sharing account ...
If you haven't seen this article already:
You may want to scroll to "Removing family members" in Apple Support's online article:
says: "The organiser of a Family Sharing group can remove other members".
Manage Family Sharing settings - Apple Support
“Note: The organiser can’t remove themselves from the Family Sharing group. If you want to change the organiser, you must disband the group and have another adult create a new one”.
Else:
If needed: You may want to try using "Safety Check" ... Apple Support's Video explains how:
https://www.youtube.com/watch?v=y9QX-0IVQL4