Why cant 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 cannot join games with him nor can i join his lobby. He cant join mines either. But i can play with my other friends fine. Unless he is in a lobby with them, i cant 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 are under the same wifi but i really need a solution to this problem. Any help is appreciated.

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