
sorry to hear that you are having problems, but it is very well known that having 2 dogs from the same litter is a recipe for disaster. many responsible breeders will not sell 2 pups together for this reason, as they very often end up fighting for top spot and sadly you will end up having to rehome one of them before one may hurt the other seriously. they may only be play fighting now while they are very young but once they get a little older it will be a lot worse. May be it would be a good idea to see if the breeder would take one back now before you get to attached to it, sorry to be the so blunt. but i wouldn't want anything to happen to either pups through you carrying on with the two of them
good luck with what you decide to do