cannot set up son's apple watch to family share, apple id is different from apple id already in family share

I have an apple watch we purchased for our son, we have a phone number through Verizon, we have not been able to use it and set it up for my son so that I can track him. I can now call him and he can call me. But cannot assign him to family share since his apple watch apple id is already set up, and I cannot set him up as a family share member with an already existing apple id, and I did set up a family share id for him, I put a request in to delete that apple id. I believe my husband also has another apple id set up in his family share , if I am not wrong. We just want to be able to connect his apple watch to a family share plan so we can track him and contact him. Any help would be great, we both just cannot figure it out, it seems like it is much harder than it should be.

[Edited by Moderator]