Hi, I wonder if you have made progress on these relatives. I think (coming from the other end) that your Henry William Shand may have been the son of one William Dourie Gresham Shand (an actor) and Jessie Louisa Pearson who married in 1856 in Manchester. They had a son and a daughter although the girl died before 1869.
The marriage failed in 1865 and Jessie married Gilbert Pitcairn Simpson in Edinburgh in 1869 but failed to divorce WMD Shand first. When this was discovered, that marriage was annulled.
But... she then divorced Shand and married Simpson in Islington (legally this time).
Henry William seems to have been known as Simpson at least in the 1881 census for Methyr Tydfil.
All circumstantial so far but possibly worth checking out?
Our interest is in whether Gilbert Pitcairn Simpson's father , William Simpson, was the son of John Simpson and Isabel Gray of Airdrie. This is still speculation!