Sorry, correction needed. I wrote:

"The link between John Turnbull, nephew, and Isabella Clague, widow, in the 1861 household is that they each had a Cregeen mother, though I haven't looked at the relationship in detail. "

That should be:

The link between John Turnbull, nephew, and Isabella Clague, widow, in the 1861 household is that John had a Cregeen mother, and Isabella was a Cregeen before she married Robert Clague.