I've never kept animals together, but one breeder I've spoken to that does, says that before he puts them back after feeding, he sprays their faces with water just to remove the rat/mouse smell from them so it's cages mates don't get confused and attempt to chow down on it. Also, if you've got one animal that's bigger than the other, the little one can get squashed, especially if they're both trying to sit on/under the heat source.
Goodluck.
