More experienced posters might be able to answer this better, but I will give it a shot. Having more than one nomination doesn't increase the chances by making your son look better. He will still have same resume/scores/gpa/etc. It will, however, give him more chances to be offered an appointment. Each senator and congressman can nominate up to ten candidates. In the end, only one from that pool of ten candidates can receive an appointment through that nomination source. If they don't receive an offer of appointment through their congressmen, they enter the national pool of roughly 2000 qualified (nominated) candidates who compete for the leftover 400-500 slots.