They are just playing. One of my Dobes did this with one of my Coton de Tulears but without the door in between. Big guy would be in his bed with his toy, little guy would come and bark at him and try to snatch his toy. Big guy growled and showed all his teeth. Little guy taunted him until big guy would get up and chase him down the hall. This went on all the time, but let me tell you, when I had the two of them at the Vet together, little guy would stand under big guy's legs and Mom was the only one who could get him out of there. When the vet tech took little guy out of the room to weigh him, my big guy was frantic until his little buddy was brought back safe and sound. They loved each other completely. Best buddies. We lost my Dobe to cancer three years ago, and little guy (Ace) still carries around big guys (Magnum) toy and sleeps with it. Doesn't want any other toy because that one reminds him of his hero. 💕
