Hello Sandra Sorry for delay in replying. I didn't check this site for quite a while.Yes, I believe that your Grandfather was my Grandfather's brother.The details you mention all tally, except that I have your Grandmother down as Martha 'Cassells'. My father is Daniel, still living in our house in Belfast, and my mother was May.
I have a lot more detail, some from my Dad and some researched by Jan -from the Australian branch of the 'family firm'.(Alexander and George's younger brother David went to Ballarat, Australia)
Anyway, get in touch and I can send more details of our side of the family and would be interested in hearing about your side.