One of the first things I do is look for wills.
These can be a mine of information.
Have you looked to see if the 3 fathers of the John you're trying to trace left any wills?
I'm not sure where these might be for Westmorland - do they now come under Cumbria?
There's a site here for Cumbria archives which I think is at Carlisle.
https://www.cumbria.gov.uk/archives/online_catalogues/ecclesiastical/wills.aspThere is a post here about Westmorland wills which might be of help
https://www.rootschat.com/forum/index.php?topic=206137.0It would seem to be not very straightforward!
I don't know the area.
I know findmypast have a lot of wills, but not sure if they cover Westmorland.
You may be lucky and find them on familysearch.org.
I had a quick look on The National Archives Discovery Wills page in case they had been proved at the PCC, but didn't see anything that fitted.
Another thing to look at is occupations.
What was the occupation of your John? Can you find the occupations of the fathers in question?
Also family naming patterns may give you a clue.
Look at the names of John's children
What was he first, and second son called?
Can you tie these in with any of the 3 fathers?
What about your John's brothers and sisters, and the names of
their children?
Can you see any similarities? Or any unusual names that follow on?
good luck!