The fifth family was the Throckmortons. They had a monopoly on polo ponies and Steuben chrystal. They controlled memberships in the elite tennis clubs and the sale of smoking jackets, cigarette holders, and leather toilet seats. They were invited to the wedding, but declined because the wooden chairs were rentals.
You're confusing the fifth NEW YORK family with the fifth NEWPORT family. The Throckmortons made the fatal error of appointing an Anglo who was not a Saxon as consigliere, and they were wiped out in the Inbred War of 1948.
The main objections to the Bocchicchios being the sixth family all seem to be subjective: they're played for comic relief, they're too small to be a powerful family, their role as peacemakers means they couldn't take part in the war. Is there anything factual (not necessarily historical facts, but just the facts of the story as set out by Puzo) in the book that is inconsistent with the Bocchocchios being the fifth of Five Families?
