The source I gave explains the succession fairly well, in my opinion. Andrew, first of Udston, was succeeded by his son, Robert. Robert, second of Udston, was succeeded by his eldest son, John. John, third of Udston died without issue and was succeeded by his brother, Patrick, making Patrick the fourth in succession. I hope that is a little clearer. There's no source indicating that Robert's son John (Patrick's brother) predeceased Robert. The source cited indicates that John resigned the lands of Brunton to his brother, Alexander and that Patrick succeeded John to the lands at Udston.