Game minimizing on another PC in same house

Hi My son, Daughter and I all have BF 2042 installed on our PC's. When one of us is playing and another goes to load up the game it minimizes the game of the other people playing in my house. Is there a fix for this or is this because we are all through the same Router? We don't have this problem with any other games we play together online or local host. 

Any help greatly appreciated.