Aggressive greyhound...?

I am currently fostering a greyhound boy who is up for adoption. I have two other dogs; a Labrador girl and a small crossbreed boy. The greyhound is very aggressive towards the other two, especially with food around. When I feed them their kibble, he snarls, growls and snaps at the other two. When I'm eating my dinner, he does the same. Any suggestions on how to alter his behavior?