Public match online split screen

Basically my friend and I want to do split screen online so I start Battleborn on my account, and he logs into a profile I made for him on my PS4 since he doesn’t have one of his own. I attempt to start the public matchmaking but it says the second account needs a PSN account, so I thought okay, I’ll have him make a free PSN account to log in to.

He does that and logs in, but we still get the same message saying he needs a PSN account, so I figure he needs an actual PS Plus subscription. So I instead log him into my brother’s PS plus account, but the PS4 won’t let him log into the account, so now we’re stuck being unable to play online split-screen.

How do you go about playing online split screen?