Few things to consider:
1) who signed the death certificate for Ann?
it is not unknown and indeed can happen often, that person signing made a mistake in the details they gave.
2) 1841 Census does indeed have Charles and Elspet as most likely group. Lillias on that would seem to have a twin.....did you find his record too? Charles and Elspet are close in age, so, although not impossible for it to be otherwise, more likely that this is a first marriage.
3) There is a younger Charles Gordon in the Kirkmichael area in 1841, in a household where there are Camerons too......may be nothing, but might do no harm to look at that one too.
4) Did you rule out that James Fleming's mum might have been a Jessie Cameron - have seen instances on death certificates where the husband's mother's name was inadvertently given instead of the wife's mother's name.
