There is a death registered in Belfast on 25th Dec 1840 for John Graham aged 73. You can view the original certificate on-line on the GRONI website, using the “search registrations” option:
https://geni.nidirect.gov.uk
You will need to open an account and buy some credits. It costs £2.50 (sterling) to a view a certificate. You can use the same site to search for Susan’s death and John’s re-marriage to someone named Edith. There are quite a few John Graham marriages in the period 1911 to 1945 but it shouldn’t take too long to work through them to see who they married. (I see one on 25.8.1920 in Belfast to Edith Brown. However that John was a bachelor, so can presumably be ignored).
The 1945 death certificate should give you John’s marital status in 1945, so from that you can search for his second wife’s death. I see an Edith Graham death in Belfast on 18.5.1942 aged 33, and another on 14.1.1968 aged 78. But there were others outside Belfast.
There’s a tree on Ancestry which gives Susan Graham’s dates as 1859 – 1920. There’s a death in Belfast that fits that on 19.10.1920, aged 61. However she was the wife of William Graham, time keeper. So not the right lady as far as I can see.
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_retu…
Post the results of your search on this board and I’ll see if I can add anything to your information.
