That's great news that on Joseph Bisset's marriage, under the name of Russell, his father Joseph Russell shows as an iron turner! That, for me, would be the last piece on the verification trail that the family down in Dumfries is indeed your Robert's family
As mentioned, you and Maggie are tracing different family for RBWR. Maggie has the family in Dumfries, you have the family in Glasgow as potential family for RWBR.
The Robert born in Glasgow to Robert and Janet (Robinson) is the one who had a sister Catherine and maternal grandmother Catherine.
The Robert in Dumfries, b.. Torqueer, is the one born illegitimate with the connection to the names Welsh/Bissett/Russell. His brother Joseph, showed his father as Joseph Russell, iron turner, which is what your Robert gave as information. His maternal grandmother was Janet Robson, the surname your Robert gave on his MC to Maggie. This Robert's sister was Thomasina. This Robert also has the right occupation and was free to marry Maggie following the v. early death of first wife Robina.
I think this might be as close as you get Trish, without visiting a genealogy centre in Scotland and going through all the Robert Russell marriage/ deaths to discout the Glasgow born one. I think his family is the one that Maggie has. All the information you have on RWBR are contained within this family.
I think you have not been helped by some of the family stories that have been handed down. Particularly that RWBR died c. 1930. As you have seen, there is nothing to support this. The fact that the family seem to have been divided in the 1920s would make me suspect that RWBR and Maggie may have parted around this time, although not through a formal divorce which in that period was out of reach for many people.
What did the 1959 death cert say for the Robert who died in Dumfries regarding wife/ves, parents, informant and occupation?
Monica