It's very doable with henchmen. Just follow these rules:
1. Take out those frost giants on top of wall first before opening the gate.
2. After the cinema, don't light up the beacon, immediately go outside the right gate killing a single group of jade armor/bow/mursaat hanging outside, and the following group of frost giants. Then immediately return to stay close to the King, never to leave him alone again.
3. Always kill those jade armor/bow/mursaat first, and ALWAYS kill level 28 bosses LAST. This target priority is very very important !!!
4. Always target jade armor/bow/mursaat ahead of white mantles, because jade armor/bow/mursaats were given strict order to head directly toward the dwarf king and have to be dealt with first.
5. Best defense position? Stay right next to the dwarf king! You'll be fighting bad guys coming up the stairs left and right. Trying to keep dwarf king in your circle so the hench monks can heal him.
I've done this mission with hench only for my mesmer and ranger characters. It's not hard if you know what's coming.
