Re: Alex mclennan married Ann mackenzie 1805
With the information you have I guess there's no way to be sure if the couple that married in 1805 is the one you are looking for. But I guess chances are quite strong.
I took a look in Scotlands People and that's the only marriage in all Scotland of an Alexander McLennan and Ann Mackenzie between 1800 and 1813. The image is not very clear, but it looks like Alexander was from Shieldaig (Applecross) and Ann from Kishorn (close to the border between Lochcarron and Applecross, and not far from Shieldaig). There is no mention of parents or occupation.
I guess this is the couple in the 1841 census:
Alexander McLennan 65 Fisherman
Ann McLennan 45
The age of Alexander is close to the birth year you mention. There's no Neil McLennan there; in fact I cannot find any Neil McLennan in Applecross or the nearby parishes, born 1813 +/- 5 years. The only one that comes close is:
Flodavery, Isle of Harris:
Neil McLennan 30 Tenant
Murdoch McLennan 25
If Neil had a brother Murdoch, then chances are that this could be him.
I'll try to see if I can find more children of Alexander McLennan / Ann MacKenzie to see if you can tie all this together.