Yes, it is a bit convoluted to follow.
After interweaving the facts that are down in the research notes into the biography, I am not convinced this is all the same person. Here's what I can gather, based on the records you have cited:
Ann Duncan, was b. 1826 to William Duncan and Ann Innes. In 1841, she may have been enumerated with her cousins, George Black & family.
In 1851, a woman named Ann Inglis, of the same age as Ann Duncan, was enumerated with the Duncan family and listed as married and a daughter.
In 1861, Ann Inglis is enumerated with the Duncans and listed as widowed and a daughter.
In 1861, Ann Black marries John Inglis. Subsequent to that they have three children. They are together on the 1871 census.
In 1901, two separate [?] deaths occur: One for Ann Black whose mother's maiden name was Robb, and one for Ann Inglis whose mother's maiden name was also Robb.
I can only see the transcriptions for the censuses and nothing for the other records, but I assume you've seen the originals.
Questions & comments:
- Where are all of these people in 1831?
- Are you confident that George Black did not have a daughter named Ann? Or is it possible Ann was mistakenly listed as a Black while staying with her cousins? I frequently see records of girls about that age being traded around to help family when someone is sick, there's a new baby, etc., so it doesn't surprise me to see her with cousins.
- Is is possible there's an earlier marriage record for Ann to another Inglis? Maybe she was recently married to a different Inglis who has work (sailor, fisherman, criminal) that takes him away, so she stays with her parents. He dies. Later she marries again to his...cousin? Brother? It would be worthwhile checking the exact date the 1861 census was taken*, since she may have remarried later in the year. Also, the citation for the marriage record says it happened in 1961. I'm assuming that's just a typo, since you have them together in 1871.
- Are those actually two different death records? Or different versions of the same record, one under her maiden name and one under her married name?
*I don't know about the UK, but in the US the census takers are supposed to use the "official census date" and enumerate where people were living in that date. In my experience, though, they usually just wrote down whoever lived there or was there for an extended visit on they day they actually showed up to take the count. On US census pages in 1850 & later the enumerators wrote the date of their visit, so that can be helpful in tracing events.
