Thanks for your answers, helped a lot but still few questions remains.

Wouldn't it be better if A recruits both B and C?
(Not sure at all about this but) then I should get:
30 levels from B to A
30 levels from C to A
when B and C hits L60?

Is the RaF bonus account or character-specific? I mean that if first toons on accounts B and C hit L60, they lose the 3*XP, but if I start new fresh toons on those accounts they still get the 3*XP bonus?

Or does the 3*XP end when the first toon hits L60?

Also this line in the official RaF-FAQ bothers me:
Also, should monsters or quests be marked as "Low Level" or listed as gray in difficulty for either character, triple experience will not apply.

so B and C wouldn't get the tripleXP, but still they would get the normal xp (from elites) when grouped with my main?