There were two William Howlands having children in Andreas at around the same time.

The first William married Leonora Fargher (1818, Andreas). They had at least five children born in Andreas between 1818 and 1825. As you say, his widow is in Bride in 1841 with some of their children and I'm pretty sure that he is the William Howland buried in Bride in 1829. The parish register entry reads:

Wm. Howland aged 33 years who met with an untimely death by the blow of the boom of a vessel and was drowned west of Pt. of Ayre May 21st

The other William married first Margaret Christian in Andreas in 1809 - there's no record of them having any children and Margaret died in 1820 (there's an 1821 will which I haven't seen yet). William then married Margaret Garret in Andreas in 1821 and they went on to have at least four children before William died in 1833. Margaret married John Quirk later the same year.

It is possible that this second William is my William's father - which would make him and John junior cousins.