Hi Rose
I think we have a result and a connection. On re-examining the 1841 entry for Luke Settle at Slead Syke, Brighouse, I find in the household Alfred, age 9 - not 7 as previously said. His mother is not listed, but I suspect this must be your man.
If so, it looks as though Ann was Luke's daughter and Alfred was taken to live with his grandfather.
The IGI lists only the one Alfred, as mentioned in my previous reply, bapt 1831, so if it's correct I think it backs up him being Luke's grandson.
Also, if this is the right bod, (assuming you can confirm it to your satisfaction) you might want to give the letters to the Trustees who run the 'Mrs Sunderland Musical Festival' annually in Huddersfield. If you've not heard of it, it's quite prestigious and there is, I believe, a special award in the name of Luke Settle, so I think they'd be thrilled to have the letters you mention. And come to mention it - I'd be glad of copies for my own family history, since Mrs Sunderland and Luke Settle were so closely associated.
Please do get back to me if you think any of the above what you're looking for and I'll give you more info on the Mrs Sunderland angle.
Regards
Lindy