I think I've deliberately blocked out all of the potty-training memories because the whole experience took forever and was so traumatic for all of us. : I do remember that one thing that helped us, and might help you, too, if you are comfortable with it, is that during the summer time, we would let the kids play naked in the backyard sometimes. We would have a little potty sitting out there ready and waiting for them. They enjoyed splashing in the hose naked, and it was quicker and easier for them to transition straight from that to using the potty than it would have been for them to put clothes on again and go inside. Maybe your son would respond well to something like that. At any rate, your son will definitely use the potty when he is ready to! I know that right now it might seem like that is impossible, but they all seem to figure it out sooner or later.
I wish I could help, but I honestly don't remember with son #1, and son #2 went poop on the potty only the 2nd day of being out of diapers (they're 18 and 15 now). Never had a problem with either of them. My daughter, youngest of the 3, was a pain in the butt to PT. Everyone told me how easy it was to train girls. Not for me! The boys were a piece of cake...lol Anyway, I haven't read all the comments, but good luck!! Like people said, it very well could be because of his brother still being in diapers. He will get it eventually. Just don't press him to do it and let him go at his own pace.