Why can't i play black ops 3 on the ps4 with a family member?

Okay. So i have my own ps4 and my brother has his own. We both bought separate black ops 3 games. I can play minecraft and borderlands fine with him online. But it seems that cod is the only problem. ITS So ANNOYING i can't join games with him nor can i join his lobby. He can't join mines either. But i can play with my other friends fine. Unless he is in a lobby with them, i can't join… And when we try to join eachother in games, it always says connection interrupted and kicks one of us out. I think that its probably because we're under the same Wi-Fi but i really need a solution to this problem. Any help is appreciated.