Yeah he had 5 sons and two daughters from the information I have, three went to Scotland and one, Robert, definitely stayed in Derry, his family were the ones that became Neely and Adair the undertakers. The monument was put up by Mathew to his father at Killea, I don't know what happened to him apart from the fact he was alive to put the monument up and died in 1918 presumably still in Derry, he would have been the youngest. I don't know if Matthew was also in the funeral business but I can find out, I know Robert's great-grandson I'll be talking to him this week sometime, his father also ran the business until he retired.
This isn't my information, I recently came across it when trying to piece together my line, which is why I was interested in John's parents. You probably already know this stuff.