For a reasonable fee, George's Birth Extract, detailing his parents, is available for download here:
https://www.scotlandspeople.gov.uk/guides/statutory-registersSelect "Births" and insert Forename, Surname, select "Male", Year Range of 1863 to 1865, County/City/Minor Records select "Glasgow City". Only ONE record should appear - George's!
The Birth Extract will detail his parents names and possibly the date and location of their marriage. Provided his parents married after 1855, when compulsory registration was introduced in Scotland, you can locate their Marriage Extract (select "Statutory Registers" then "Marriages"). It should detail the names of George's grandparents. Good luck.
We will remember them.