Many thanks for your interest.
I have 4 certificates relating to Andrew, 2 give a birth year of 1835 and 2 give 1837. I have a death certificate for Thomas which gives his date of birth as 1836.
Henry was definitely Andrew's first child born 1864, followed by William Gunn in 1866, James Andrew in 1870 and Mary Christina in 1877.
regards
RussJ