The "remove member from family" option is not available - even though I am the parent

I have set-up family sharing for me and my 3 children (10, 12 and 13 years old). They all have their own AppleID which I set-up for them and connected to the family account.

There are 2 problems that I am not able to solve:

1. my oldest child got a new iPhone. All data was transferred from the old to the new. I removed the old iPhone from his AppleID and wiped the device completely. Still, this device shows in his "screen time" overview and states that is has not been active for more than X days. Yes I know - I wiped it, removed it, cleaned it... why is it still showing in his family sharing/screen time menu? How do I get this removed?
2. On the forum I read that if you want to remove a family member, the guardian has the option to click "remove from family sharing" in Settings->User Name->Family Sharing->Name of family member. This option is NOT VISIBLE for me - even though I am the parent / guardian of the family. Any ideas on how to fix this, or what could be the root cause of this?

In general, family sharing/screen time is a hugely desired functionality for me and I like the concept, but the user friendliness of this functionality is not as smooth as I am used to from Apple in general and there are quite a few twitches/bugs/hurdles with this software.... recognizable for other parents...?