Hello! My name is Julia and I have a 10 month old husky named Blu. I recently moved him to my sisters house about three weeks ago, because I have decided to move in with her. I'm moving in with her this weekend, but wanted to wait until my semester was over. We both though my entire moving process would be easier if I moved him with her first, since the distance is about 7 hours long. She's a mom of three young boys, and has a four year old golden retriever. When I first took him there their dog, Jagger, did not like Blu at all, and bit him a few times. However, now she says since I have been gone he's gotten very territorial over her and gets angry whenever Jagger comes around. She says Blu has snapped at him when he walks next to my sister, and sometimes gets angry when one of her sons comes around. At first I thought maybe he needed some warming up to do, but she keeps saying that his behavior is becoming mean. When she talks to me about him, I swear she's talking about an entire different dog. Blu has always been so sweet and loving to me and other dogs. He adores my sister, but when she disciplines him he gets angry and chews things up, or uses the restroom in the house. It would be really useful if I could get some advice. I'm hoping he acts better when I move back this weekend.

Thank You,
Julia

Blu is heading into his teenaged time where they become brats and push the boundaries of everything and if your sister doesn't mean it or doesn't time it right or lets stuff fly because she's nervous when disciplining him he will take advantage. Especially with a new person essentially that he's never had to listen to before. Some could be her behavior toward him triggering things. If she is nervous or getting that way then he is going to push her harder. She needs to tighten the rope on him, not let him get away with things. How does she usually discipline him? How does she handle the two dogs? She needs to give her dog attention and food first and make Blu wait. Establish herself and the other dog as being there first and that he can't change that by being a brat with a poor attitude. Most of the attitude should pass in a few months until he grows out of being a teen. Until then, treat him like a new puppy and basically start training him all over again.

Everything Jenn said is spot on.
Keep in mind that Blu just had his/her world turned upside down, and at a very difficult time.
Blu got moved to a new home. Blu lost the person he used to live with. Blu now has to compete with another dog. Blu has all these new people thrust into his/her world. Blu is at an age where he/she will challenge everything.

This is a lot of change all happening at once. Blu is likely lost and confused as to what is going on, and needs a strong, firm set of rules to get established into this new situation.