If this is the John Crain/Mary Crain in the 1870 and 1880 census of Jackson, Ripley County, Indiana, I suggest you try to find more information in Indiana before you try to go backward to the Isle of Man.

Try to get an exact date of death for both John and Mary, or possibly for their children, probably from Ripley County records, and then go to the local library and search the newspaper for an obituary (or you can do this by mail/e-mail if you live at a distance)

You can locate Ripley County death records, if available on microfilm, by going to Familysearch.org, and clicking on "Library Catalog", then click on "place" and type in Ripley county, Indiana. They can be viewed at any LDS (Mormon) Family History Center, for a small fee.

I think it is risky to assume John and Mary were married in the Isle of Man--they could have immigrated separately with their parents, and married in New York. Most Manx tended to settle in areas with other Manx families, and further, they tended to marry within the Manx group.

I think you will find your search on the Isle of Man much easier if you collect as much information as you possibly can about their time in the United States, before you try to cross the ocean.

Good luck!