Taunt does work on the nictus but once they get out of a certain range from romulus they will go back to him. trick is to find the range.
Also I did this battle for an exceedingly long period of time, the healing nictus would heal the nictus' and Romulus if close enough to everyone. It was easier just to kill Romulus the 4 times and have a tank on the nictus keeping them far enough away not to be able to help Romulus. Each time he resses he takes a nictus with him. Seems to be the first one is the spawning nictus, then the AoE nictus, and last the healing nictus.