the museum is a one-stop shop for all pre 1900 records - everything is there
The probable line seem Rushen based
Hen Watterson + wife Margt Nixon son Mark + wife Margery Kinley son Mark + probable wife Ann Harley (m Rus 1849) anne's mother is in castletown born Scotland in 1841
Margery Kinley was prob d/o Richard Kinley + cath Nelson(Kneale - nelson being a common anglicisation) m Rushen 1789
You can search these people on www.imuseum.im
The Kinley family has been well researched and many wills etc are on www.manxnotebook.com
The Nixon family should also be easy