According to Henry Macnab's service record he was bc.1790 in Aughagower, Mayo, Ireland and enlisted aged 18 on 4/5/1808, discharged 5/6/1816.
At least 21 trees on Ancestry claim he was born 1785/6 but I would think his service record is more likely to be accurate. His death certificate does not appear to have been found as his death on the trees varies between ca.1861 Melancton, Ontario, between 1861 and 1871 Grey, Ontario and 1870 Simcoe, Ontario!!
I agree with Sancti in that a religion of 'Church of England' does not fit with someone Irish or Scottish! One tree I looked at had 'Thomas' living in London in 1790 and with his wife dying in London in 1825?? They also had her born in Yorkshire in 1762! Another tree has Thomas born in Dull, Perth in 1762 and not Aberdeenshire. Most trees just seem to be copies of each other!
The only definite with this line is that Henry himself is said to be born ca.1790 Aughagower, Mayo, and there seems to be no 'proof' of who his parents actually were, let alone his named siblings.
Without said proof of exactly who to be looking for it is extremely difficult to pursue this one.
Annette