The rule is that 7 ndranghetisti can made a ndrina and 7 ndrine can create a camera di controllo (Chamber of Control) but this happened decade ago.
If a ndrine was created in 1950s every sons of the members become automatically members to the blood ties plus plus if the members have daughters them must marry a sons of ndrangheta members or a man that deserve to be made and their sons will increase the ndrina numbers.
Out this people that form the Minor Society there are those form The Santa and the Mayor Society. So is difficult to say the exact numbers of ndrangheta men and who is the real boss because in Canada the ndrangheta exist from the 1930s and with no rats there are no infos on the structure.