PS Plus accounts - I just don't get it?

PlayStation Network / PlayStation Plus accounts:
I have a PS3, PS4 and each of my 3 kids have a PS Vita.
I understand you can have 2 PS Vitas tied to one PS Plus account, but even so, one brother playing against the other on a game like Minecraft doesn't work too well, one has "Mobs" that the other can't see?
With 3 is impossible. So I've set up 3 separate ps plus accounts. (Yes, it's costing a fortune), now, when we get the free monthly games, do I seriously have to download 3 copies of the same game to the PS3, or PS4 - or am I simple?

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