Hi Lynne

Don't worry i had to look back myself , and got a little confused.

I was referring to the MC (Marriage certificate) of James Crebbin and Jane Cowley Jan 1, 1861. The original hand written by the Vicar is on the LDS IGI site and clearly shows his father as William. James is illiterate, and there is a user sponsored listing showing his father as Thomas. But the MC is clearly William.
I am assuming that you think this James has returned to the IOM, which is possible.
Again I could find no birth of a James Crebbin to a father William on the IOM from 1828 to 1843, so the James Crebbin who married Jane Cowley could be your James Nelson Crellin.
It is a shame that nobody has been able to tell us the background of the two William Crebbins who died in 1840. If one was yours, it could explain that Sarah went to England with the two children after his death. I think your line moved to the Liverpool area like a lot of Manx people did.

Cheers
David