[2020] I could use a little help

So, me and 3 friends got 76, all 4 of us enjoy it, but we have a private server and only 2 of my friends are on my fallout friends group, and I only get the option to add the third as a friend, but it never goes through. We have been friends on Xbox, and the others were already there, so we are all just lost on what the issue could be, but if anyone has dealt with something like this help would be appreciated. I’ve tried looking everywhere to no avail