Hi Poodlz, I don't know if you have these records, but you can confirm the deaths of Donald Grant & Agnes Tait by downloading the certificates from scotland's people. They will give both their parents names and therefore take you back a generation. They may also shed some light on the Simon Grant Mackenzie connection. The death certs I've picked out are only suggestions, but to me look the most likely. I could, of course be wrong.
1881 Parish 99/2 Kilmonivaig, Lochaber
Donald Grant /74 /Shepherd /Contin
Agnes Grant /68 /Kintail
John Grant /30 /Kilmallie
George Grant /25 /Unemployed Shepherd/ Kilmallie
Jessie Grant /21/ Dom Servant/ Lochalsh
Eliza Minings /77/ Wife of Clock Cleaner/ Born at Sea
Alexander Campbell /21/ Servant/ Kingussie
Donald Cameron /25 / Under Gamekeeper/ Employee/ Kingussie
1881 – 1891 Donald Grant b. 1807 +/- 5 years: 6 deaths in Inverness; 2 possible ones in Lochaber, his last known address
1899 Lachlan Grant rented Kindrummond, annual rent £72
http://digital.nls.uk/directories/browse/pageturner.cfm?id=85909998&mode=transcriptionhttp://www.mocavo.co.uk/The-County-Directory-of-Scotland-1893-1896-Volume-1893-1896/935227/3021891 District 96A Dores, Inv sh, Kindrummond
Agnes Grant /76/ Farmer’s mother/ Kintail, Ross
Simon Grant/ 41/ Farmer’s brother/ Kilmallie
George Grant/36/ Farmer’s brother/ Kilmallie
Jessie Grant/ 28/ Farmer’s sister/ Kilmallie
John Finlayson/ 16/ Farm Servant/ Croy
Cath McKenzie/ 15 Dom Servant/ Contin
1897 Agnes Grant, other name Tait, born 1817, died Croy, Inverness shire