Dear M.,
I'm a mother of 4 children and I've come full circle on this issue. First of all I just want to say that potty training can be extremely frustrating because you know that your child knows what to do and when to do it, but THEY are in control, NOT YOU. When I finally realized this and relaxed, everything got better and easier!
I have 3 boys and 1 girl. Girls just get it sooner and are easier in my opinion. After my first boy, I don't even attempt to start the potty training until they are 3 yrs. Now, that doesn't mean that the child won't come to you and ask to be trained and start going by himself. If he does and insist on big boy pants, then that is great, job done and no sweat to you. I have discussed this with my peditrician and he was relieved and said that he wished all mom's had my attitude. I know it may be hard because you have loving Grandma's telling you what and how to do it. Go with your instints and relax. Don't worry and he will get it. As soon as you back off, he will probably start going again.
One other suggestion - once you're committed to potty training you should get rid of all diapers. In my opinion, pull-ups are just fancy diapers and your child knows it. You will have to deal with many accidents, but he will get it. He has to have the accidents in order to learn. Also, night time training is different than daytime training. Sometimes the child will stop wetting the bed at night when they potty train and sometimes they don't. BE PATIENT!