My Dogs and the window ISSUE!?

I have 3 female dogs however this is just typically between my Boxer who was the 1st dog I had and then my Mastiff/Rottweiler mix which was my 2nd dog I purchased....Now my Boxer of course since she was the 1st seems to think she is the QUEEN B of the other 2 however whenever my Mastiff tries to look out the window she will growl until my Mastiff backs up. She acts as if this is HER window and no one else can enjoy it. Realizing this is a dominance issue how in the heck do I get her to quit doing this? She also does this at times when my Mastiff is trying to be with me..as if I am ALL hers! My Boxer is very dominant/jealous! Now as a side note my 3rd dog which is a Great Dane doesnt really seem to have a problem with her and my Boxer acts as though it is ok if she wants to look out the window..almost like she babies her as if she was the baby. Part of me feels like my Boxer has her panties in a bunch because a few times my Mastiff has definately put her in her place!