I think I'm pretty clear on Mary Keating, who became John Tobin's second wife after the death of his first wife Margaret (nee. Roach). There was a significant (20 years) age difference between the two, and I know they did not have any children.
Mary Tobin - I'm not sure that she was John's sister as both were born in 1809. A cousin perhaps? Was Edward Keating Mary's brother? As I said, I'm curious. What information do you have?
I have been unable to locate pictures of John Tobin although I would love to see one if one can be found.