Topic: Using content on 2 PS4's at the same time

Hi. Hasn't had much luck getting a proper answer on how this works or how to go about it properly.
I (Dad) have a PS PLUS account, and my kids (x3) each have a std PSN account, linked to mine as child accounts. I have 2 PS4 consoles.
For example I would like to be able to play Minecraft (purchased on Dads account) on both PS4's at the same time, with the kids accounts. Kid1 plays on PS4(a), and Kid2 plays on PS4(b). Not necessarily online, but a LAN game.
We used to be able to do this, but something changed and it doesn't work.
ATM, on PS4(a) log on with Kid1, start Minecraft. On PS4(b) log on with Kid2, all games locked. Says needs to be activated as primary. Unable to activate as primary as another PS4 is primary. If I deactivate PS4(a), PS4(b) activates and works, but PS4(a) doesn't work.
Its a stupid system! Any help would be much appreciated.

@GrumpyDad111 you need to use the child account on the primary PS4 and the account with the license on the secondary PS4. An account without a license can play a game if the PS4 has a primary account with that license. The account with the license can play on any PS4 that is connected to the Internet regardless of whether or not it’s their primary PS4.

Thanks for the reply. So, 2 child accounts can't play at the same time? My account (the one with the license) is on both.

@GrumpyDad111 That is correct. The child playing on the secondary PS4 will have to use your account.

Thanks a bunch. Makes more sense now, but like I said, its a stupid system! I'd have to make one of the kids a main user, don't really want to do that when they are all under 10! Don't really want to purchase 2 copies of every game for 1 household.
Sorry for the rant! Thanks again.