Sure thing Vincenzo would have been horrified, to learn of his brother Frankie's "betrayal of omerta and his own Don" [not public knowledge? at that time] unforgivable infamia in their honour is everything! world

and Vincenzo would have come to Washington on his own accord
Quote
Kay: What really happened with Pentangeli Michael?
Michael: His brother came and helped

Kay: I didn't even know he had a brother. And where is he now?
Michael: He's on a plane back to Sicily

Kay: All he had to do was show his face
[Michael nods] It was between the brothers Kay -- I had nothing to do with it!

Frankie was jolted and reminded of omertà by his brother Vincenzo's presence, his piercing icy stare was knifelike
Made Frankie realise, what he was about to do - betray his Don - is a no-no in the business they have chosen and need to honour the omertÃ