I have to agree with SpartaDog, RTB's and Ball Python's would never come in contact in the wild, one is from Africa and the other from South America. It's not a good idea period whether your friend's snakes are doing fine or not, it doesn't make it the proper way to keep snakes. I would spend the money on another cage or just not do it, remember not every snake is the same your's could get stressed easily or not but again why take the chance????