According to the "Graves of the Fenwick Church" Andrew was 80 when he died and Christian was also 80 at her death. Making her birth year about 1808. I show that Andrew was born in Stewarton and Christina in Galston (according to the Census)
Their youngest son John Gemmell b. May 9, 1851 (a second John as the first John died at age 3 in June 1845) married Janet Montgomerie born about 1865. Their children are:
Andrew b. abt 1885 Fenwick, James b. Jan. 15, 1886 Bobbingworth by Ongar, Essex, England d. Jan. 4 1962 in Castlegar, BC, Canada (married Annie Mary Edgar),
Martha b. June 12, 1887 in Fenwick d. 1955 (married Hugh Craig b. 1877 in Ayrshire - all their children were born in Essex, England,
John b. abt 1889 Fenwick, William b. July 22, 1890 Bobbingworth, Essex, England,
Christina b about 1893 Bobbingworth,
Robert b. abt 1894 Bobbingworth,
Hugh b. March 4, 1895 Bobbingworth and died in March 1986 Eppling Forest, Essex, England,
Frank b. abt 1897 Bobbingworth,
Janet b. 1899 Bobbingworth and
son b. about 1900 Bobbingworth.
One of Martha Gemmell Craig's desc. immigrated to New York, USA.
There is a Will for Andrew Gemmell d. 1880 in High Gainford, Fenwick on Scotland's People. I do not have a copy, but if you want to download it go to: scotlandspeople.gov.uk (for a reasonable fee)