Ah - the honeymoon period is over. Most books I have read on dog on dog aggression say it takes 4-6 weeks to manifest itself. I is kind of hard through cyberspace to really see how they are acting, but I can give you a few pointers that my behaviorist gave me with Penny Lane and Leo.

You should never give treats, chews, or food in each other’s presence. They should be totally separated.

If either shows any antisocial behavior (growling, snapping or being nasty), they should be given a time out either in their crates or another room away from the pack.

Both dogs should be on the NILIF program. They get nothing without saying please and thank you (sit/down/stay/wait, etc).

They should be separated if you are not watching them completely. They could possibly get in a nasty fight over something as minor as a piece of paper that has your scent on it.

I would also strongly suggest contacting an animal behaviorist to evaluate your dogs’ behavior toward each other. They will be able to tell you if it is going to be manageable. They can also put you on a behavior modification program to help the dogs learn to get along.

I am not going to lie to you, it could be something that might take a year or more to work out - or it could be something that you can't work out. A behaviorist will be able to help you decide the best way to tackle it.

Good Luck and I am sorry you are going through this. It is a very difficult situation to be in.