Hi Christine

He is missing !!!

I started with the marriage of John Muncaster and Ruth Hellen ,( From IGI) 25/12/1790 Saint Bees, Cumberland , England. Children :
Joseph 9/10/1791
Mary 8/9/1793
Eleanor 20/4/1794
Thomas 26/6/1796
Ann 24/3/1799
All the above at St Nicholas, Whitehaven, Cumerland, and possibly at Moresby, Cumberland
John 11/10/1800
Then
John 30/1/1803 Kirk German
Ruth 11/8/1805 Kirk German
Elizabeth 5/7/1807 K German
William 17/6/1809 K Lonan
James 26/11/1815 k German

I looked for a birth on the IOM for Isaac with any surname 1805-1820 and although there are 10 , but none look like the one you want.

James is shown as a death 3/6/1816 by both the IGI and Brian Lawsons burials.

So as William was born Lonan , looked for him and found two marriages , but neither show the father's name.
18/1/1833 Braddan
17/5/1836 Malew

Marriage of Issac and Elizabeth

Andreas 4/7/1833

Isaac Muncaster of the Parish of German to Elizabeth Wade , a minor with the consent of parents.
They appear to have at least 10 children , including Isaac Gunson ch 17/8/45 who is not with them on 1851 census and is not on te burial list, and very odd for the time, a Scott ch 11/9/1851.

Not much help for what you want, but maybe something you did not know.

David, Sydney