Sounds to me that you are enforcing this behavior in your dog. Here are your words...

The aggresive nature appears when ever the dog is seated on the sofa while we are around, if any of the cats gets even whitin sight the dogs starts to growl. If a cat comes in close quarters to the dog , the dog attacks!! I think he is trying to be possesive over us.
Get the dog on the ground and off the furniture if this seems to be when the problem occurs. A dog who does not realize you don't need protected is what you are looking for. Show him you don't need protected and higher your position in the pack in his eyes by showing him as the alpha you sit on the couch and he sits on the ground. You go out the door first, eat first, everything first and you should see his tendency to protect you diminish.

Good Luck!