Well, having bored everyone in my search for my gr.gr.grandather's death, and the family graves, I got there in the end, last week Thanks to everyone who has posted on this thread, and especially thanks to Lodger, because of your posts I knew what I was looking for. OK, the remains of my family have either been lost forever in the 60s, or moved with so many others to New Monkland, but it was still worth it.
Ironically I'd gone to Paisley because of a funeral and decided, rather than do the sensible thing and start the trek home, I'd head back east on the motorway and turn off to Aidrie. I found the new Wellwynd Church quite easily, but there was nothing in or around there that looked as if it could have ever been a churchyard then realised the part that Lodger had photographed was on the other side of the road. Now small, walled off and rather sad, but the inhabitants being those who could afford lairs and headstones.
I spent some time in the library. "Go upstairs to see Alan in Local History" they said (I'm sure it was Alan?) and what a knowledgeable and helpful man! I explained that I'd not found any record of my search for Thomas's death (through Poor Relief for his widow Margaret) at the Mitchell, and he suggested that I sat and went through the records for the 18 months time period, looking for entries for mortcloths. He set me up on screen and left me to it, or so I thought, though before he left me he gave me a brief masterclass in interpreting Parish Relief records which was so helpful.
In fact whilst I was scrolling through, he was double checking the records I already had by way of census, birth etc and by the time I'd eventually ploughed through and found nothing, either for Margaret as a widow in her married name, or in her own name, he had the maps of the area for 1850 all ready.
When I, in my naivety a few years ago, had googled 37 Aitcheson Street and decided it had all been swept away in dual carriageways, he'd looked at the town as it was then. He was able to show me exactly and sent me off to walk up hill to where the house would have been - even to tell me the type of house, poor crowded tenement, no surprices there. The area where I had thought 37 must have been was was totally wrong, because the buildings - and numbering - were completely different then.
What he did show me was where it had stood in relation to the town - high on the hill, on the very edge, facing green and the hills. Mines very close both in both directions and no way of knowing which one Thomas was killed in, or which on my gr. grandfather James lost his hand in. He also explained that the housing there was rented by room, and not owned by the mines so the address gave no clues either.
I walked up there and found the spot on the corner of Aitcheson Street and Sword Street. Modern housing now of course, and a housing estate opposite where it would have been common ground and mines looking on to the hills. He was right, it did help. The 2 boys in the family, James and Thomas, must have been hungry and cold much of the time but they had grass and fresh air immediately outside, they weren't down in the centre of the town. Didn't stop Thomas jnr dying of TB at the age of 7 though.
So that's it. It really is a brick wall. My 18 month window for Thomas snr's death following a accident in the pit, between late 1849 and spring 1851, was too early for local paper reports of mine accidents, too early for death / burial registration, not mentioned in Parish Relief. Having been to Aidrie LIbrary and had such comprehensive help and answers to my questions, I accept that now.
I had to head home in the end, because it was work next day, but will go back to Ryden Mains to the mass grave one day, and go to Greengairs and other Aidrie addresses.
For now, I'm so grateful for the professional and knowledgeable Local History section of Aidrie Library because even though the answer has proved to be "we'll never know" I did learn something, and I'm so glad I went.
