PS: The gas chamber is no big deal. The masks are so secure, they actually have the SRs pull them away for a minute so that they can experience the gas just a bit. My son's mask was screwed up, so he got more than his share of the gas, and even that was no big deal. Fear not!
I just read your question about the last name for PIR issue. If you are all four attending together, it will probably not be a problem. Just take proper ID for you with a photo, and if you can find something that has the other (wrong) last name on it, even if its just an old library card or something, take that with you too. If you have a copy of the list (with the wrong name on it) take that with you. When the MPs at the gate ask for IDs, just show them the correct one, and the paper with the wrong name on it. As long as 3 out of 4 people in the car match the list, and you have current info, it will probably be ok with the guards at the gate. I would just hand them the IDs - and get on base. Then when you check in at the desk (much more mellow than at the gate) you can easily explain that your son just goofed up. The guards at the gate are concerned with security, not seating.
As a former police officer, please don't worry about the gas chamber. It's over in a heartbeat but tell all of them not to keep tissues in their pockets and then use them! That's what I did all those years ago and then I irritated my eyes with the gas soaked tissues. I''m not the brightest bulb I guess.
You will find this site very helpful and full of members who are eager to answer your questions. Browse around the site and check out the forums, groups, blogs, photos, videos, and even the other member profiles!