As Pentangeli stated, Ola was Roth's "sicilian messenger boy". But I'm sure he was a capo in a NY or Chicago family assigned to provide muscle for Roth. I see Altobello as a Don (afterall,he was Don Altobello) going way back "as your family's oldest friend". I find no indication that he was a Corleone family member.

As far as Zasa succeeding Pentangeli, there is no Board consensus in what year the events surrounding Pentangeli's demise took place. Since III took place in 1979 or there abouts, it would seem that Zasa was indeed too young to have succeeded Pentangeli as of 1979. However, if we accept that Zasa was easily 40 years old in 1979-80, then we can play with the years and might be able to put Zasa at the Corleone helm in the early 70s if not the late 60s.