Me again Heather
Alexander Jack married Catherine Jack m/s Jack 8 Nov 1821 Avoch. I cannot view the OPR marriages on S P for 1821. They are available but only by ordering an extract for 10 GBPounds. Same applies to Donald and Flora's marriage, they give you the dates but you can't view them. The OPR's would probably/usually give you the wife's father's name.
In the meantime here are the children (may not be all) for Alexander and Catherine:
Alexander MacKenzie Jack b 16 Sep 1823 bapt 27 Sep 1823
Donald Jack b 1 May 1825 bapt 19 May 1825
Alexander JAck b 11 Aug 1828 bapt 21 Aug 1828
Catherine Jack b 21 Oct 1830 bapt 7 Jan 1831
Margaret Jack b 30 Sep 1832 bapt 3 Oct 1832 ( your GG/Grandmother )
Alexander Jack b 3 Jan 1835 bapt 23 Jan 1835
Simon Jack b 3 Jan 1835 bapt 23 Jan 1835 (Twins?

)
Mary JAck b 12 Dec 1838 bapt 16 Feb 1839
Isabella Jack b 5 Nov 1841 bapt 8 Jan 1842
I hope that this will be of help to you
Joy
PS I'll start on the census hunt - perhaps tomorrow
