I was trying the allow my daughter, and then wife to play with me. Neither could get logged in or create a character. You had said this was fixed.
Still needs work.
I played couch co op with my wife and it worked fine, I think both accounts have to have associated blizzard accounts. In diablo 3 it wasn’t necessary. Hope this helps.
I played couch co-op all weekend with the wife. Only caveat was that her account needed to be associated with a battlenet account.
Login times for her to join was horrendous on Saturday, with no UI indicating progress. But it works, and was much better on Sunday.
Were their PS or Xbox accounts linked to their BattleNet accounts? If not that was probably the main problem.
If so, then they were most likely in the login queue, which is only problematic because the UI doesn’t give you ANY indication of that, if you are trying to join someone else’s game. THAT is something they need to fix.
Husband and I spent a good hour or so on Friday night getting everything setup so we could couch co-op, and it took us finding a Reddit post to figure out what the hell was going on.
As others have said you had to link your Xbox account with battlenet.