My 4 year old rescue German Shepherd is so afraid of meeting new people he shakes when he is around a lot of people. What can I do?

I have two dogs. My first is the younger of the two, she is a Rout/Beagle mix who was trained as a pup to work with handicapped children. She is well trained but sometimes refuses to go outside because she escaped once and the pound picked her up and had her for a week. My second dog just turned 4 and is a GSD. He is papered and was neutered. He is leash and house broken but does not respond to commands like sit, stay, and come. Is he to old for obedience training? He is very well behaved and non-aggressive. He is incredibly timid and visibly shakes when he is in a store or around lots of people. I am extremely interested in buying the basic obedience video, but I want to make sure the video will work for a 4 year old GSD and a 3 year old mix.

I have had the GSD for only 6 months and the rout/beagle for 1 1/2 years. I want to keep my dogs for a long time, I am a pastor and I need well behaved dogs, is it to late to train my dogs new commands? I am a new dog owner and inexperienced in training animals. Is there another video that you would recommend. I do have a prong collar for my rout/beagle. I use it only on walks and correction is rarely needed. She was a puller/tugger until I got that collar and her attitude changed considerably.

Thanks you.
Rob
South Bend, IN