Bulldogs World

Hello,  We have a 6 month old bulldog and his name is Baxter.  My question to anyone is - He is very aggressive towards my other dogs and he is growling at us and the dogs.  How do I stop this?  I always feed Baxter alone because he is a puppy and was feed three times a day.  I didn't want the other two dogs to steal his food.  I can take his food away from him and he doesn't do anything, but if the other dog comes close to him he goes crazy.  He was born with a #3 heart mumur so I think we totally spoiled him because we did not want to stress him out and now I think we have created a little monster - a beautiful monster but never the less a little monster.  If we go on walks he is great with other dogs and people.  If anyone has any advise please let me know.  Thank you very much! Georgina