I've just recently dragged out a big binder of records that I transcribed several years ago from the Rc Parish of St Andrews, Braemar, Aberdeenshire, from 1703 to 1757.I transcribed every McKenzie record that I could find, male, female, godparents, etc. I've been going through them alphabetically, by location, they lived in many little hamlets in the area around Braemar.I'm gradually getting them into family groupings, as best I can.After the 1st Jacobite rebellion there was not much of a slow down on the Catholic baptisms, which were done in secret, as the priests were in great danger if caught.After the 1745 rebellion, however, it seemed the baptisms started to dwindle off.Not immediately, but by 1750 it was noticeable, and more and more so, until they "ended" in 1757.That is any records that I'm aware of ended, for the area.I don't know that baptisms ended, possibly they couldn't be done by a priest, if there were not enough priests, or maybe it was the danger factor.They didn't resume again until 1781, and your Mckenzies would have been in Ireland before that time.
I'll look for McKenzies in the area with John & brother James; there would be several families, the trick is to find those that may have disappeared by the time the baptismal records resumed in 1781.
If your John Jr was born abt 1783 in Sligo, I'd think that his father was likely born in the late 1740s to mid 1750s, although hard to know if we don't have other children, or know birth order, or age at marriage, etc.The McKenzies involved in the Jacobite rebellions were not exclusively from Braemar and area, but they were staunch supporters there.
I'm trying to get this straight, however, and there must have been 3 generations involved here: the 2nd Jacobite rebellion was in 1745. Anyone involved in the rebellion would have to be abt 20 years of age, or older. That puts date of birth around 1725, or before.However that wouldn't be John who had son John born 1783, he'd be in his 60s; so likely John & James were not themselves involved in the rebellion.I'll try to find parents with children John & James McKenzie born around the time of the rebellion, who maybe were sent as a family to Ireland.
On the other side of my family (I had my 2x great-grandmother Elizabeth MacKenzie, from Braemar, and have her traced back), was her husband, also a MacKenzie.John MacKenzie & Elizabeth MacKenzie were married in Dundee in 1833.John was the son of Lewis MacKenzie & Janet Stewart, living on the Lintrose Estate near Kettins, Forfarshire, in the early 1800s.It's said though that John's father, Lewis Mackenzie, came from around Glenshee, to the north of Kettins, and not too far from the Braemar area.As well, it is said that his wife Janet Stewart actually came from Braemar, originally.
Likely this doesn't make a lot of sense, I've been working on all this for quite some time. If they (your ancestors) were from that area, which is quite likely, I may be able to find something on them, now that I'm going over the families again with a fine-tooth comb, so to speak.
No guarantees, but will let you know if I find anything of interest.I know that is not giving you anything concrete, yet, but hopefully it will reach that point.I'm up to my eyeballs in MacKenzies (McKenzies, Mckenzies, M'Kenzies, however they spelled their names), right now, and don't have them sorted out, but hope to eventually.