Sanna, Just closing the loop on this one and recording our offline conversations here. Yes, I do now definitely believe that the James who erected the headstone to his uncle James CROSSER, was indeed James the son of Archibald FAIRBAIRN and Alison CROSSER. And is the same James referred to in your kind posting of the 1854/5 Sassine referring to Elizabeth LAIDLAW relict of James FAIRBAIRN late of Lantonhall and formerly Clarilaw. And is the same James at Sloethorn, Selkirk in the 1841 census with assumed children Alison, Archibald, James, Barbara, John, and Walter.
All of these children have recently been found in Canada and the States, some now as FAIRCHILD. And even better, James' brother David also emigrated and descendants have been found in Canada, and America.
Which only leaves the 1797 John (of the known children anyway) to be found.