Do a search and you will find plenty of reasons why not to house them together in one tank. You will also find reason why it's ok but I think the risks far outweigh the benefits that some claim.
Correct me if I'm wrong but isn't 3 mice in 7 days for the smaller and a small rat for the larger one a bit much? Our bp is just over 3' in length and has filled out nicely and she eats a small rat which I think is a tad big for her. I just can't imagine a bp that is a foot smaller than mine taking the same size prey. Not saying it can't happen or anything...just kinda surprised.