But not all the underbosses/caporegimes would agree with that. If the son become boss they were passed-over. Maybe they are gonna betray the family (like Tessio).

Bonanno wanted his son as successor but the commission didn't agree, neither did his caporegime (or underboss?) Gaspare DiGregorio.

It doesn't happen often, the only examples I can think of in NYC are:
John Gotti-Junior Gotti
Carmine Perisco-Al Persico

Santo Trafficante succesor was his son Santos Trafficante, Tampa.

In Sicily i think it happens more often than in America.