There probably shouldn't even be orcs in Minas Ithil during this time period, but perhaps Cel's memory is acting up. In anycase, history won't save you here.
Start by terrifying the orcs. They are a superstitious, cowardly lot, after all. They have a superstition, for instance, that it's bad luck to have an elven super warrior stab you eighty-seven times in the spleen. But since optional objective one is to Brutalize at least four orcs- stab away.
You can Brutalize more than that, or terrify the rest of your quota with morgai flies and ghuls.
Your second optional objective is to take out the Fear Eater's bodyguards. This isn't too hard, as taking out mid-thirty-level captains go, but it is a trap. When both are down, the Fear Eater is empowered by vengeance. Dark vengeance.
You won't be able to Dominate him until this rage passes, so settle for roughing him up (you shouldn't have to watch your back too much, since you've already terrified away the orcs in the area). When he breaks, Dominate him any way you like for mission completion.
