Multiple cat owners, please answer.?

After my 12 year old cat ped away in May, I brought home a kitten to my 15 year old cat that I still had. The old guy took to the kitten right away. There was no having to keep them separate to "get used" to each other. They bonded immediately, snuggled together and groomed each other etc. It was great. Now, the 15 year old ped away and the kitten, who was now 6 months old seemed so lost without his buddy that I decided to get a shelter cat, which happens to be the same age as him. Again, there was no having to separate them. They bonded immediately. HOWEVER, the one I had will NOT let the new guy near US. He gets real nasty and chases him and will even bite him if he tries to come to us!!! Will this ever stop? I can't believe how they get along with each other, yet, he's so jealous if the new guy even looks at us for too long. What can I do to stop him from picking on this cat for trying to come near us? I have to tell you, I can't put him in a cage while the new guys comes to us. I know he loves us and I don't want to reward his love by putting him in a cage, yet I'm at my wits end about having this other poor fellow being chased all over the house and bit because he too wants to be pet and loved. ANY help will be appreciated.