I need some advice as to how deal with my dogs?

I have a 3 year old Shih Tzu named Gucci. In August my chihuahua died so I decided to get another dog to keep Gucci's company. Instead I got 2 puppies, a chihuahua and a mixed terrier. I thought that Gucci would have been glad for some company but he is being very aggessive towards the puppies. I have gradually introduced the puppies to him by letting him sniff the behind like I see on Cesar Millan. Somehow that is not enough because he is growling at them and I am afraid he is going to bite them. I am hoping that you guys could share some ideas.