Yes, please attach a photo of the headstone or the text from the headstone.
Scotlands People is where you should be looking
https://www.scotlandspeople.gov.ukDEATH CERTIFICATE for Alexander Graham 1863 is available from Scotlands People.
It will tell you if his wife Ann was still living when he died.
Also the following marriage record -
MARRIAGE 04 April 1762 Kilninver and Kilmelfort
John GRAHAM to Marjory McMILLAN
Also the Baptisms of children:-
Archibald 08/12/1762 Kilninver and Kilmelfort
Duncan 03/03/1765 Kilninver and Kilmelfort
Marjory 12/07/1767 Kilninver and Kilmelfort
Un-named male 18/05/1770 Kilninver and Kilmelfort
I dont believe the un-named male born 1770 will be your Alexander.
Birth year of Alexander Graham from records -----
1841 census (Ages were rounded in this census) born abt 1781
1851 census born abt 1779
1861 census born abt 1778
1863 Death born abt 1777