I'm allergic to pine, carefresh, and several other beddings. I've had the best luck with Aspen, Cellsorb, and just plain towels (although the towels have to be changed and washed daily with the rats) I've also heard good things about using newspaper (with soy-based ink), and paper towels (Again with the changing daily)

Also, why not use a large-grain sand so you don't have to worry about them eating it? I've seen a lot of gerbil setups where they used sand or sandy soil, and the gerbils really seem to enjoy digging in it. I'd probably just go with newspaper for the hamsters: it's cheap, easy to get, and they'll love shredding it.

Edit: Don't give up after trying just ONE other bedding, try as many as you can until you either find one that works or find out that it is the critters after all.