Big thanks to Gilthresa for putting these together, and allowing me along for the ride!
During the Baron Ashbury encounter he will cast an ability called Stay of Execution, for the achievement he must not heal using this ability, so it will needs to be interrupted a split second after he casts it. Just repeat this through the whole encounter – There are also two other things that will need to be interrupted, these are Mend Rotting Flesh and Pain and Suffering, interrupting these will make the encounter so much easier for the healer and will make the achievement much easier.
To the Ground!
For this achievement you must not let an add cast Unholy Empowerment on Commander Springvale, to do this you could assign two people that can interupt to a certain add when it spawns, or you can get two tanks and pull Springvale out of the room and keep him LOS from the adds, making sure that one tank picks up all the adds that spawn. This will cause them to never cast Unholy Empowerment.
Lord Godfrey will randomly spawn adds during the encounter, these are the adds you need to kill with Pistol Barrage, simply have your tank drag the adds through Pistol Barrage and they should die, be mindful that the tank will take an exceptional amount of damage and to counter this it is probably best to use two healers.