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I wonder if all those births at different locations are consistent with the same family ie was Donald described as a Slater in each location. Of course he could have worked at any occupation from time to time.   Another matter is regarding the DNA study.  Big Toshie and I both had ancestors from Glenurquhart and the yDNA study showed our families were related but further back than our family trees reached, and there were 2 other testers from the glen who matched us.  Another group of 3 were from a different Mackintosh/McIntosh DNA family.   If there was a male McIntosh descendant of the family in question they could at least test their yDNA and find which family from the glen they matched.

Thanks Ben
That did not help your quest at all but a group of us Glenurquhart McIntoshs have a similar halpogroup to Somerled and I thought there may be a connection.
Incidentally, there is a descendent of Robert McIntosh, No 18 in your text in our DNA project.
Regards
John Mc

Have you tried to search British army records held at Kew in London?  I have paid researchers there a modest fee to look up army records in the past.  There is also a searchable database.   

Another avenue is yDNA testing.  I am a co-administrator of the McIntosh DNA project so send me a PM if you would like more information.

John Mc

There are two McIntosh families from the Isle of Skye in the McIntosh DNA project database.  Google McIntosh DNA project.  They appear to be unrelated. 
John Mc

I don't specifically know of this family, but I descend from a Glenurquhart McIntosh.  There is a yDNA project for Glenurquhart McIntoshs and we find so far 7 of us group into 2 separate McIntosh families.  The yDNA test requires a male to be tested.  If you have a male McIntosh relative who was willing to participate I would pay for a 37 marker yDNA test with FamilyTreeDNA.  If you would like more information contact me with a personal message
John Mc