I honestly do not understand how (after reading any of the manuals provided by community) you can still fail but i'll try to help you

Very basic example for shamans:

Master:
#Showtooltip
/cast Lightning bolt

Slaves
#showtooltip
/assist focus
/cast Lightning bolt

it WILL work if
1) your toons are in the same group
2) all your slaves have master as focus
3) The facing/range/not silenced etc... do not prevent to use the said ability