Debbie, I still think your best bet would be wills, especially because there are not many for Benson, and these are usually very informative. They often name siblings or other extended relationships which can identify where someone fitted into a particular family. I listed these for you in a previous message, in your other thread:
These wills included what looked like the will for William's wife Esther.
The LDS film numbers were on that list, and these can be ordered for a small fee to view at any Family History Centre, worldwide. See in phone book under Church of Jesus Christ of Latter-Day Saints. (Or see the films in the Manx Museum Library.) - But best to get as much information as possible before visiting the IOM.