I have overlooked I think an important Census in 1881 that you found of Henry William at Glenmuick, Tillich and Glencairn.
That census in 1881 in Glenmuick etc is
irrelevant, because that's the Henry McKenzie born in Maryculter and you already know he isn't yours.
1881 Census: Glenmuick Stable Yard, Glenmuick Tullich and Glengairn, Aberdeenshire
William MCKENZIE, Head, 48, Gardner Dom, born Dingwall, Ross and Cromarty
Mary MCKENZIE, Wife, 47, Maryculter
William MCKENZIE, Son, 21, Gardner, Maryculter
Henry MCKENZIE, Son, 12, Scholar, Maryculter
John MCKENZIE, Son, 10, Scholar, Maryculter
Alexander MCKENZIE, Son, 8, Scholar, Glenmuick
Mary MCKENZIE, Daughter, 5, Scholar, Glenmuick
George FORBES,G Son, 3, Aberdeen
His father is employed as a domestic gardener, not the owner of the estate. The 1885 valuation roll lists William Mackenzie as inhabitant occupier of a house at Glenmuick. This means that he was in a tied house that went with his job as a gardener.
The owner of the estate was James Thomson Mackenzie but this does not mean that William was necessarily related to James Thomson Mackenzie. In any case it really doesn't matter because it's not your Henry Mackenzie to start with.
I think his brother Alexander born 1794 in Boharm graveyard.
Alexander Mackenzie who is buried in Boharm kirkyard died in 1874. So he is almost certainly the Alexander McKenzie, mother's maiden surname Fowler, who died in Mortlach in 1874 aged 80.
There are two deaths of William M(a)ckenzies with mother's maiden name Fowler: one aged 60 in 1860 in Inverness, and one aged 68 in Urquhart and Logie Wester in 1878. The one in 1860 obviously isn't the father of your Henry, who was born several years later, but the one in 1878 might be. Either could have been his grandfather. You need to look at the death certificates to see if the parents' full names match.