The two that are easier to get to were done previously. What we did to get to the one behind the dash was pull the vent to the left of the airbag, pull the airbag and remove the glove box.
From there you are able to see the actuator behind some steel and a wiring harness and below the vents. Used a pry bar from the opening of the airbags to GENTLY lift up on the vent since it sits right on top of the actuator. Got a small socket in there to get the two screws out and remove the old actuator. Putting the new one in was not as bad as getting it out. The front screw was pretty easy, that back one was difficult but the guy helping me had a magnet that he was able to use to get the screw positioned and a few hand turns tightened. We were really worried that screw was destined for a life at the bottom of the firewall.
The rear one was quite easy. Hardest part was getting the panels off.
The behind the dash actuator was 89018365 ($277)
The rear one was 89018375 ($174)
You can get actuators a lot cheaper either after market or possibly getting a fake from Amazon. As much of a pain in the ass as this was I was not willing to risk it.
These were purchased at the GMC dealer.