How to detect traps

There is a trick to disabling some of the traps in that area, you probably already found it. This disables enough of the traps that you can cross the area, but not all of them:

Light all the braziers in the adjacent room to disable some of the traps

You should be able to disarm the traps if you select only a single party member and click on them when the mechanics icons appears. I've no idea why this doesn't work in your case. Though I'm not sure if you can disable these specific traps at that point, my character wasn't able to actually disable them.

You can get your party across through the traps by moving each one individually. Just click on the portrait of one of your characters, you'll only move this one then. It's a bit annoying, but possible. There is also another way around the whole thing, so if you don't want to bother, just look for another way out of the cave.

As of Patch 1.03, you gain an additional 10% XP for every empty slot in your party. (i.e. 5 party members = +10% XP, Solo = +50% XP, etc.)

Keep in mind that there is a level cap, and substantially more XP in the game than is needed to reach it. Keep in mind also that the higher level you are when recruiting NPC's, the more decisions in their development will have been made - often poorly.