2 PS4s at home - question on sub accounts and multiplayer games like Titanfall 2

Hi!

I'm still really confused on how to set up two PS4s at home.

PS4 a: The original - a Pro with my account and three sub-accounts (fiancee and two kids).

PS4 b: The new one - a Slim. I signed in with my original account above and transferred most games. The subaccounts transferred over. I also created a brand new main account and have PS+ on it.

I want to play Titanfall 2 on both. I want my main account OR the subaccounts under that to be able to play on either system. If we try to start Titanfall 2 on anything other than my original main account on the Slim PS4, it says only my account is licensed for it.

Fair. So, the big question:

Under what account do I buy Titanfall 2 again so that the sub accounts can play on either PS4?