Yes John McCain served, but do you think he did so because it was the family business?
“ But Annapolis, with its regimentation and lockstep curriculum, would provide no such opportunity. Annapolis was a commitment, more so for McCain because of the family tradition. Under the law he could get out of the Navy four years after graduation, but would he? Here he was at Episcopal, feeling himself drawn toward a school he despised by forces he felt incapable of challenging. Was there any reason, then, to believe that after four years at Annapolis and a similar period as a naval officer he would be able to defy those same forces — whoever they were, whatever they were — and resign his commission to embark on some new, ill-defined career path?”
(C) 1999 Robert Timberg All rights reserved. ISBN: 0-684-86794-X
I don’t really know, I know his father was an Admiral in the Navy as a Submarine Commander and Later Submarine Squadron Commander and served with Distinction. He participated in the U.S. Torch Landings in North Africa and then rest of the war in the Pacific.
So it is possible, as you note, that John McCain was told by his Naval Father that he “would serve in the Navy” and that was the end of that. So would he have joined if the decision was left up to himself, maybe not? Nobody will ever no for sure.