Can't remove members from family sharing after changing my phone.

I set up family sharing for my kids as a way of managing their purchases and keeping an eye on what they wanted to download. When I sold my iPhone I forgot to remove the family members from the group and now, I don't have an Apple phone anymore, I'm a bit stuck! My Wife has an iPhone, so I want to make her 'family admin' but I can't remove the kids from the group. When I send an invitation from the Wife's phone, it tells me that they are already member of a group. If I sign in as me on my son's new iPhone and try to disband the group, the option is greyed out!

I'm stuck, please help?!