Jealous Dog. Training Tips?

I recently adopted a five yr old dog from my local shelter. I have two other dogs that are very well socialized and good with dogs, cats, horses, etc. At first, all three dogs got along very well. However, when i pet or play with my other dogs, the new dog starts barking and will eventually attack them if i continue to pay them and not him attention. Does anyone with experience in the realms of introducing shelter dogs to existing dogs have any behavioral training tips to help my amily out?