[ QUESTION ] what happens to my brothers purchases if I Set my PS4 as his primary system

okay I'm looking to play a game that has downloaded from his account and it's locked.

I found out the only way to play it in my account is to set my PS4 as his primary.

will doing that let us have the ability to play multiplayer together or play it separately or will the license lock on his PS4 as well?

also since he has his own PS4 will setting my PS4 as his primary leave him with no ingredients ? Will he be able to download his purchases like games themes dlcs from his own PS4 on his account