To my knowledge, only one domestic airline (Frontier) permits cavies in the cabin. The others simply don't want rodents to share the same space with the passengers. Most airlines will only permit dogs or cats to be carried in the passenger cabin, especially in light of the recent misuse of the "support animal" provision where people were carrying all sorts of critters in the cabin. This means that your cavies will travel in an approved container in the cargo hold.
You should be able to go to the individual airline's website to find posted information as to an approved carrier. I simply wouldn't want to check my boys as cargo in any kind of potentially extreme weather as the heat in the summer or cold in the winter. You have no way of knowing how long they will sit on the tarmac when they are being loaded/unloaded on the airplane. That can especially be potentially dangerous if there is an enroute aircraft change to a connecting flight. I'm not trying to scare you, but having worked for an airline for several years, I feel as though I have a bit of an insight into the process.
If I were you, I would investigate another way of transporting them such as FedEx, Airborne, etc. In any event, ask lots of questions in advance of shipping your piggies.