The order of births on the family tree I have goes like this. (no dates)
Martha, Alexander, Margaret, Rev James, Robert, and John.
Only exact birthdate for that family that I have is: Rev. James Septimus Mairs born 30 Mar.1839.
John and his wife Margaret had a baby they called Robert Alexander which leads me to believe that there was a Robert. They also had a William.
Children of John and Margaret (in case you don't have all of them):
1. Anna/Annie Matilda Mayrs (3 July 1882).
2. James Mairs (5 Aug.1883).
3. John Black Mayrs (29 Aug.1884).
4. Margaret Letitia “Maggie” Mayrs (26 Feb.1887).
5. William Black Mayrs (18 Apr.1889).
6. Robert Alexander Mairs (1891)- died young.
7. David Kennedy Mayrs (24 May 1892).
8. Joseph Charles Mayrs (27 Sept.1895).