Does this describes the information you are giving in this, and earlier post when researching the origins of your Donald McKENZIE? -
You have a letter dated 5 July 1875 from Ronald McALISTER, Minster of Dingwall, being his response to enquiry by A Wilmot McKENZIE in India, and seeking information about the family of Donald McKENZIE native of Nig, Rosshire, and this Donald died in India about ten years earlier (than 1875).
Rev McALISTER in response names four brothers, Alexander, John, Robert and William, and three sisters, Lillias, Isabella and Catherine for your Donald who died India.
"I have recently obtained the birth certificate for whom I believe is my Donald McKenzie.
The certificate states that he was born and baptised on the 2nd September 1797.
His father was Kenneth McKenzie (a weaver) and no mother is listed."
If this Donald McKENZIE, baptised 1797 has father Kenneth, then you might expect that the Donald referred to in the letter, 1875, with brothers Alexander, John, Robert and William would also have a brother Kenneth, named for father, Kenneth?
Do you know the purpose of the enquiry to Rev McALISTER in 1875?