ДНК S05E81 - Выпуск 640. Сваты проверяют внуков

For eight years now, the whole Ponomarev family has been living on pins and needles. The grandmother and grandfather doubt three grandchildren, the father doubts two children, and the mother herself doubts only one son. So which of the three children bears the surname Ponomarev by right of birth, and not only by documents?