In Russian the middle name is the patronymic. Thus, the middle initial is the first letter of the father’s first name. And, as in many languages, the first initial is the first letter of the first name.

Below are the names of a Russian family's names:
• A.N. Petrov
• B.M. Petrov
• G.K. Petrov
• K.M. Petrov
• K.T. Petrov
• M.M. Petrov
• M.N. Petrov
• N.M. Petrov
• N.K. Petrov
• N.T. Petrov
• T.M. Petrov

Draw the family tree of the Petrovs, given that every father has two sons, the patriarch of the family has four grandsons, and his sons have two grandsons each.

Prove that the solution is unique.

Source: Tanya Khovanovna (sans solution)