Progress is continuing!
I now have the 1857 death certificate for Janet MacDonald, my 3x g grandmother, and so information on her parents and one of her daughters, Isobel.
Can I ask your opinion on James McIntyre, the 1826 Kilmallie baptism? I've attached the record and I don't think he's a sibling, despite the parents' names. The record notes 'in fornication' - all the others are 'lawful', as you would expect with an 1800 marriage. It's also in a different place and, though I'm not certain of the handwriting, this Colin may come from Strone?, Fort William, not Morvern. There are two Janet Macdonalds and one Colin McIntyre of the right ages in Kilmallie so I'm leaning towards coincidence rather than relationship.