Hi Sue,
Sadly, a good two hour perusal of the Frances Will Summaries has, frustratingly, produced nothing. That is to say, nothing that immediately jumps out at you. I've took heed of what you say and looked closely at the detail--'to my best friend' 'to my three sons' etc and I can't glean any new information from my study. That does not mean the information is not there, it's just very difficult to spot.
I've had a look on the 'familysearch.org' site for the marriage of William and Elinor Christian in 1802. There are two other Williams married in Maughold around that time. One on the 30th Oct 1802 to Margaret Kermod and another on the 10 May 1800 to Catharine Kelly.

There are also five non-Maughold marriages which are;- 1800 Kirk Michael,
1800 Michael
1801 Andreas
1802 Braddan
1803 German.

I have also ascertained that Dorothy married a John Dorman or Dormon or Doron in May 1838.

Unfortunately, none of this gets us any further forward. If only William had been called Apollo or Melvyn or even Humphrey!

Thanks again,

Tony