I am sure you have solved the mystery !!! Lynne will be very happy.
I had been looking for a William Crebbin with father James as Sarah had called the first and only daughter after her mum, so I was thinking William may have named his son James after his father.
After you posted the burial of Isabella Ann with Mary Ann , my immediate thought was who is Mary Ann, and had started looking and you have done that.
Mary Ann is correctly shown as 1837 on Brian Lawson's burial site. Is there a way that Brian's site can be corrected ?
Now we have to find what happened to Sarah (Fell) Crebbin.