are they all the same level?
are they all partied with your shaman?
as long as one is linked to you, you both will get 3x exp. unless there's a bug, that's how its supposed to be.

so with..
Main refers A
Main refers B
Main refers C
Main refers D

you will get 3x as long as main is partied with any of the four new accounts.
note, they will not gain 3x exp if they are partied together wihtout the main.

i would have done it differently, but well you gotta work with what you have.