Let’s handle the easy one first. VP noms should be applied for at both. USNA and USMA essentially do the choosing for the VP. There is a statistical possibility he could receive a VP nom to both. It’s an independent process from the state elected officials.
For the state elected officials, much depends on how they set up their application process. Some allow a candidate to apply for every SA nom, some ask for a ranking of SAs, some collaborate amongst themselves and “spread the wealth,” not giving multiple noms to the same candidate. Add this in to whether they use the principal nom, ranked slate or unranked slate method, and it’s a minefield of uncertainty.
Your DS should do his best to be absolutely clear, from his research on the websites and discussions with staffers to resolve questions, on what their process is. He should proceed accordingly. If ranking is requested, I strongly recommend being consistent in the order across all nom sources, not trying to game it by flip-flopping it - the staffers talk, and it’s hard to explain yourself out of. If he has to rank, he should make a choice, but it would be fine in interviews to note he has applied to another SA, they are very close in his mind at this stage, and he would be honored to have a nom to either. Keep in mind there are some states where more than 1 nom is not achievable due to the collaboration.
One stage of worry at a time. If he doesn’t get a nom, or doesn’t get an offer of appointment, and he really, really wants this, he will execute his alternate Plan and re-apply. These forums are filled with college re-applicants. The SA incoming classes are well-stocked with re-applicants. If he does college ROTC, and is a great cadet or mid, that’s a nom right there, and a year of college, additional maturity and ROTC training under his belt.