Hi Colin, bad news I'm afraid. No sign of a baptism for any Usher's in Malew between 1814 and 1820 (inclusive). Any from 1821 onwards should have shown up on the IOMFHS/Lawson's list of births I would have thought.
I looked at the Will of Henery Usher who died on or about 29th May 1765 in Malew. He died intestate, and three announcements were made re his death but no relatives came forward to deal with his effects, so his principal creditor Ewan Looney was given the task. Hard to tell what his trade was from the difficult to read list of effects but there was mention of 2 looms & swift & whill & a spool, so perhaps a weaver, or maybe a netmaker??
There's nothing to connect him to Jane Usher (1759-1843).
Also looked at Malew marriages 1819-1822 and 1811-12. No Usher's there either, although a lot of soldiers from Castletown/Castle Rushen barracks appear, including a Mr Hornbloa!
Sorry
DavidR