Once you make sure there is no elites you can group them around you and use your hammers to reduce the cooldown of falling sword and recast it as soon as it comes up. I'm not sure if i just got lucky but when i was right on top of them the mortars they cast did not hit me and just went over my head ( so hopefully you can get close and not worry too ). The elites do have a cooldown before they cast another set of mortars that you can get close to them and hopefully kill them before. If you find a mortar elite you can use your horse to run out of the mortar impact zone if you need. The key to beating the set dungeon is to carefully attack groups to make sure there are no mortar elites in the pack. If you can get Gabriel's Vambrace (bracers) or Guard of Johanna (shield) those would be better to use but i did not have and didn't want to spend time trying to find them just for this set dungeon.

This is probably not the best build possible to beat this set dungeon but it was perfect for what I had in my stash.

I just beat the set dungeon for the Seeker of Light set and this is the build i used.

Diablo 3 crusader light set dungeon