Yes, there were a lot of Janes. The complete family was
Charles Joughin, their father, lost three daughters, one in 1788 and two in 1794.
Although the wife of Caesar Caine could have been 1799 Jane, your #1c, it seems perverse to make that connection as Charles and Annís family were in Andreas, whereas your #2 was from a family already in Peel, where Jane and Caesar were married. The household recorded in the 1851 census at Kirk Michael Street, Peel also makes better sense if visitor Jane Agnes Joughin was Mrs. Kaighinís first cousin, rather than a much more distant relation.