Apple Watch series 8 cellular using apple family setup issues with cellular connectivity

I purchased 3 Apple Watch Series 8 GPS+Cellular for my kids for Christmas. They were purchased through AT&T and a cellular line was added to my husband account for each watch and we upgraded his account to whatever the top one is. Each watch has their own cell phone numbers and we’re activated. I don’t want the kids to have phones just yet so I used their apple id’s and Apple Family Setup to sync them to my iPhone 12 Pro which is on a different AT&T plan (which according to Apple should not matter because we are using Family Sharing). Everything works fine until the kids leave the house. They are sometimes able to make calls and send texts from their watches but it is very inconstant and sometimes outgoing texts get stuck for hours. Sometimes I can track them and the watch using the Find My app and sometimes one will not move from a location all day long and the other two have moved and they were all together in the same car. I have called AT&T a million times and same for Apple. I have unpaired, factory reset, repaired, check the OS versions, paired to a different iPhone, turned off and on the watches, the phone, tried airplane mode, removed the cellular carrier and added again. Nothing works to provide consistent cellular connectivity.  We have no issues at all on wifi in the house. The only answer AT&T gives me is that I should add my iPhone to my husbands plan. He has an android phone so he can’t sync them to his phone. I can’t be the only person with this problem?