For me, I will be leaving Mirys at cap for the time being. Mureall is due for a more capable build, even if unarmed monk isn't the technically best now. As of now, I am literally 6 quests away from ETRing Mureall, at which time she'll be ready to TR.
Build wise, I'm still torn between a Wolf-sploiter, some unholy abomination involving Ranger levels, or some unholy abomination involving Paladin or Fighter levels. Needless to say, the build will be some unholy abomination. I intend to remain unarmed because she's geared out to level 24 for it.
I think the theory is some of us either TRing our current mains or plugging in another character depending on desires/insane ramblings. We begine to alternate between the current/future TR group, and a second, likely "epic" group every other week, with the current alts being brought in same as now. Or we switch between the two low-level groups until the next TR cycle, whenever it hits, at which point I'll bring Mirys around as a Vanguard.
In my case, Mirys remains at cap, until the next TR wave. Mureall replaces her in group A as the TR (depending on how much I play Pillars tomorrow and Friday, maybe before-hand). The difference between your '3' is that instead of one main group, we switch between two, every week or other week depending.
Of course, I could change my mind, since Mirys only lacks the capability to ETR (not sure where I am on karma, but I think I'm almost there for the Arcane sphere). In which case, we'll have either a Fighter or Paladin Vanguard (probably Paladin pure). I already have most gear, just need shields.
Also, we sacrifice a goat. Or a Honda Civic. Whichever.