Free trial and full game on same ps4? or even just multiple accounts

So my flat mate asked earlier about the ffxiv free trial. as was concidering giving the game a try. the question is as I already have the game downloaded on my ps4 would he be able to use that with his psn ID if he registered it on mogstation for a trial thingy.

and if he were to then upgrade would his psn id work on my ps4?

or would a pc trial work on my already installed pc client?

the other option was create a new character on my account but the issue there lies in that we wouldn't be able to use both characters at the same time.

PC trial definitely works on a full PC client, I've already tried that. PS4 I don't know about for trial as never tried that, but the full game (on his PSN) would definitely work just fine.

Definitely don't put him on your account, apart from breaking SE's rules (account sharing), you'd have massive problems later if they wanted to keep playing since would be unable to move character off to a different account and would have to start over.