Hi Al,
Glad to be of some help

Yes, I will check Queen Street again, next week and get back to you. It was only a very quick look as I was running out of time. I thought they should be there.
Did you notice John Crichton age 11 on the census? John Crichton was born to John Crichton and Isabell Sinclair 10th/27th April, 1839 in Dundee. Wonder what happened to the first John. Perhaps he died?
Also on the Census, not sure who Martha Jack, Mother-in-Law would be, perhaps you might know.
I wouldn't worry about the different spellings of the name, it all depended on who was recording as to whichever spelling was used. High levels of illiteracy in those days!
Unusual you can't find the family on any of the later census'. Just a thought, I see that James Jackson, Matilda's father was born in Ireland. Might just be possible that Alexander, Matilda and family went over to Ireland sometime before the 1871 census?

I had a look for deaths on SP, but there is no sign of a Matilda Crighton (any spelling) which would fit in.
Anyway, will get back to you next week.
Dorothy