Hello Ana
I don't yet have the death certificate for Murdoch. However I believe he died between 1865/66 and 1871.
In 1871 the family were living in Clay of Allan, Fearn, ROC and there had been two new additions - Angus (aged 8 in 1871) and Murdoch (5). Since the head of the household is now Ann, this sets the boundaries for Murdoch's probable date of death .
Frustratingly for me, Isabella is not living with the family in 1871. As I also cannot find details of her birth the only record I have of her early years is the 1861 census.
I cannot find the family as a unit at all in the 1881 census so my guess is that Ann died in those 10 years, and the family scattered through work or marriage. Without going into a long story, my trace back to the family was through Margaret, or Maggie, and I cannot find for certain either her or Isabella (or Isabella's first illegitimate child who was born around 1875) in the 1881 census so I'm not sure what happened to any of the children after 1871.
I guess from your comments that you either live, or were brought up, in this part of Scotland. I have never visited it myself - the closest being a holiday South of Inverness and a weekend spent in Thurso (which is where my mother-in-law thought her mother came from). She doesn't yet know that I now think her roots are further South, and maybe this will provide an excuse to visit.
Thanks again for your interest.
Kevin