IGI lists 7 children of John CALLOW of Onchan:
John bp 14 Feb 1785
William bp 17 Jun 1787
Edward bp 10 May 1789
Jane bp 1 Jan 1791
Thomas bp 1 Sep 1793
James bp 7 Feb 1796
Matthias bp 24 Dec 1797
None state mother's name.

On Brian Lawson's Manx Lawson's site I found in the list of burials:
John CALLOW 73 Onc 10 Aug 1835.
which could be him. No will in the will index though.
I found later burials in Onchan for William and Thomas which had ages matching very well, but I didn't copy them down. You might check there.