How to get into Raedric’s Hold

Don't think so; the NPC's with little Soul Vignettes are, I think basically the result of a Kickstarter pledge reward:

NAME AND DESIGN AN NPC (Non-Player Character). Help us design PROJECT ETERNITY! We will send you a PROJECT ETERNITY NPC character sheet for you to fill out for our design team. We will turn your personalized character design, with your name, class, and race into an NPC in the shipped game (within reason of course)

Based on the Kickstarter, there's about ~115 of these, and while they provide some nice lore, they aren't gameplay objectives.

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.