Sonny is present at the meeting where Tom briefs him and the Don about his trip to California. He is also present (for the most part) with Hagen and the Don at the wedding where the guests are asking for favours. Clemenza and Tessio are present at neither of those things. So, although blood certainly played a part wouldn't his presence indicate that he was a part of the family's administration?
Sonny was part of the family's administration. He was made a caporegime in the mid 1930s and possibly underboss around 1940.
