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.
"It was between the brothers Kay -- I had nothing to do with it."
