We also have 3 cats, and one of them gets very jealous. We have Tasselhof (male, 10 yr), Kittiara (female 9 yr), and Daphne (femaile 4 yr). We had Daphne for about a year when we took the other two from my mother-in-law. Daphne gets mad when I pet Kittiara, and she is quite angry that Tasselhof has started to sleep in be with us. She tries to get as much attention as possible.
To help, we have a special toy that only the two of us play with. Daphne likes to chase my feather duster, so when I get it out, we play. It helps a little.