Though this puts me in the position of rationalizing bad writing:
Probably Harrison's "we" is the Corleones with Archbishop Gilday, who assured him that he was confidently speaking for the Pope and whatever Board of Directors Lucchese and Kleinzig represented. Hence the "formality." If the Pope was being poisoned by Gilday and his conspirators, then, as Kleinzig said, "all bets are off," and Gilday would have gotten his bailout without having to make good on the pledge to hand over Immobiliare to Michael.

Lucchese's use of "fleet" is an awkward euphemism for control of Immobiliare's board: "We’ll gladly put you at the helm of our little fleet. But our ships, must all sail in the same direction." I inferred that "fleet" meant the various business interests of Immobiliare's board that may or may not have been included as part of what Gilday promised Michael. The line served no purpose other than for Puzo and FFC to try to inject some "fancy Old World idioms" into a feeble script.