Again, I don't know why I didn't find this in my searches but it is the correct record. Thank you so much. Poor Henry died in the Poorhouse. His mother's name Green is different to the one his gives on his marriage record (looks like McGarrigle) but his occupation, wife and father's name confirms it's him. It reads:
Henry Bonar Quay Labourer widow of Rose Anne died 1876 December sixth 11 hrs 35 mins am Poorhouse Greenock. Father Hugh Bonar (occupation illegible) deceased. Mother Helen Bonar M.S Green. Cause of death Cardiac Dropsy. Informant was the Poorhouse Porter.
Perhaps his father remarried. It also rules out the possibility that the two girls could be living with their grandparents. I am guessing they were in the poorhouse too or living with other relatives.
I have a possible 1891 census record for Catherine boarding at 3 Cameron Court Off North Street, Anderston, Glasgow. Catherine Bonnar aged 19 born abt. 1862 Renfrewshire Greenock - Laundress Servant.
I also found a possible marriage for Mary Ann in 1895. She would have been well into her 30s but the groom was living nearby in Dalrymple Street, an address associated with my Greenock family. but when I bought the record, it wasn't correct. This Mary Ann Bonnar was a widow.
Anyway, I am a lot further forward than I was thanks to everyone who has kindly taken the time to look for me.
Many thanks!