As long as there's enough room in the bag for them to both lay down comfortably and they don't mind being that close to each other, I don't see any reason they can't. It'd probably be easier to carry one bag than two :thumbsup:
I carry Bijou and Casanova in a huge bag all the time. He sticks his head out one side and she sticks hers out the other side. It's pretty hilarious looking, actually.
You just need to make sure there is room and they won't jump out.