So was Pentangelli's brother kidnapped by the family in Italy? Or did he himself understand and accept the risks?
Good question.
Its believable that the Corleones wouldn't have had to resort to making the actual threat.
They may have worded it so, on the surface, it appears that they required Vicenzo to come to the hearing hoping that his presence will lead to Frank feeling shamed and therfore cease in his treachery towards Micheal.
The threat was implied. But Vincenzo's facial expression and Frank's response clearly shows (at least to me) that it was all about their family's honor.
I think the Corleones had two cards to play: The family honour card and the threat to Vicenzo card.
The latter made it so the former was undoubtedly going to work, whilst at the same time saving face for everybody. Expertly played by Micheal.
In 'mafia-speak" there is a way to make Frankie's brother know he was needed in D.C. without the need for threats or kidnapping.
"Io sono stanco, sono imbigliato, and I wan't everyone here to know, there ain't gonna be no trouble from me..Don Corleone..Cicc' a port!"
