Are you sure that the putative father of Henry was the Merchant John - I'm not at all convinced - there is a complete gap in arbory baptisms between 1680's and 1728 - the register is also worn, unfortuneately the marriage of John Taubman + Margt Moore in Feb 1757 (day worn) is one of the last before the 1757 act came in to play which would have required indication of residence. Most of their children were baptised in Arbory (not Malew), one in Rushen (unusual for Taubmans) - given typical age of males at marriage then it is quite reasonable that John was born prior to 1728 in Arbory. If he was from a moneyed family in Malew I would have expected some note in the register - you need link the Malew John to Henry and that link is missing as far as I can see.

The sick Henry in Mathew's will I think died shortly afterwards - there is an arbory burial of a Henry that fits. However Malew property records should indicate if he acquired Mathew's proptery in castletown - I transcribed the 1760-1784 manorial roll of Castletown cottages but doesn't appear in that
(btw your program needs demormonising - IoM, England is a bad sign of IGI)