I would say that is the correct Monaghan family in 1881 in Scotland. So they were in Yonkers, New York by 1905, and Irvine Johnston was living with them, having married their daughter Jane. The 1905 census says Irvine had been in the USA for nine years.
That is the only time that I found Irvine and/or the Monaghan family in the USA. There was an online tree that said John Monaghan had died in 1921 but it did not say where and did not have a source of information so may not be correct. I was guessing it would be in the USA.
John Monaghan‘s mother‘s maiden name was Janet McNeill, his father Henry. He was a police constable when he married Jane Goldie in 1877 in Scotland. He was a carpenter in 1905 and had been in the USA for 22 years. He was born 1853 in Kirkcudbrightshire, Scotland.
This morning, I found a JohnMonaghan, carpenter, in the US city directory in 1908 10 Palisade Ave., Yonkers.
Just now, I think I found John and his wife Jane living in Norwalk Fairfield, Connecticut with their daughter Jeanette, born New Jersey,who had married Michael Delaney. Mother Jane had had five children, three living. Two of them would be this Jeanette and their son Robert, who is on an online tree as living until December 14, 1954. Mother Jane reportedly lived until July 27, 1930 doesn’t say where.
But what happened to their daughter Jane and her husband Irvine Johnston,? Could they have died in Yonkers before 1910?