Question on Master leveling in two leagues

So, I was thinking, if I run daily missions for 2 Masters (Say, Elreon and Zana) in Beyond, and at the same time do daily missions everyday on Hardcore for Vorici and Catarina, when league merge happens, do I keep all four of them? I know GGG posted an explanation somewhere in the announcements or patch notes but I cannot find it.

Basically, does the game:

1. Determine which league you have overall more "experience" in for the masters, and replace them all?

or

2. Pick the higher of the two, per Master.

I'd very much like to level 4 at a time or more.

Thanks.