We've done the rats-and-snakes-in-the-same-room thing here, and it worked just fine, except that the rats do develop an odor if you're not cleaning them two or three times a week. Please remember that 1.2 rats in a ten gallon tank can easily become over twenty rats in a ten gallon tank in short order if both females drop litters close together! That's kind of a lot of rats for a ten gallon tank . . .

If your females drop litters a week or so apart, the younger litter may not do very well, as they'll be outcompeted by the older ones at the teat.

~Bruce