Don't know if this will help or hinder your query regarding Lord Deas. I've just started trying to assemble a family tree with the help of some notes which a great-aunt wrote and I'm becoming more confused by the minute. According to my great-aunt, Sir Frances Deas, Baronet of Lathrisk, Falkland married Margaret Reid who died leaving no family. Sir Frances then married Sarah Outram (daughter of General Outram Of India). Sir Frances later became Lord Deas, Solicitor General For Scotland (portrait hanging in Parliament Hall, Edinburgh).
......but.....having looked up various web-sites and finding the site of the Latter Day Saints - I've found information which is similar, but different!! Apparently, people can submit information to the site, but who is to say mistakes don't occur? So.....according to the site, it was George Deas (Sir) who married Margaret Reid and had four/five children. On the site, it is George Deas who has dates 1804 - 1887 - which ties up with your information and according to the site - Georges father was called George and/or Francis and one of his sons was called Francis. So you can see I'm confused! Did my Great Aunt get the family's names muddled or are some of the details on the site incorrect? For the moment I'm still trying to work it all out! I think my next step is a visit to Register House - I'll keep you posted!