I think there is possibly a mix up of two families here
There is a John Hewitt born 1787 died 1843 age 56 married to Mary Wilcock at Rainford on 17.7.1812
they have following kids
Eliz 1810, Eliz 1812,Mary1817,Sarah1818, then alice,william,john,margaret,peter,james,john and catherine 1840.
They lived in Shuttle Alley Prescot in 1841 and John was a watchmaker.
There is also a John Hewitt born 1789 died 1866 age77 married to Mary Marsh at Rainford on 1.7.1810
thier children were
Alice 1813, Ann Black 1815,Mary 1819, Thomas 1822, Joshua 1824, Jane 1828-1867
They lived in Atherton Street Prescot in 1841 and in 51/61 John is a widow at the same address, this John was a watch and chronometer maker
Mary Hewitt nee marsh died 1845 age 49. The witnesses at thier wedding were Elizabeth Marsh, Mary Hewitt and William Browne.
This John Hewitt died 17.10.1866 after paralysis of 6 years at Atherton Street and was attended by his son Joshua Hewitt of Bromfield Terrace Coventry. There was probate of under £800 to Thomas Hewitt engine fitter of Crewe, his elder son.
Take careful consideration of the birth and death dates of the Johns the marriage dates and the spouse names, they are all mixed up in your details and also the tree that is on Ancestry.
Going on this info I think I may have a possible parents for John Hewitt b1789
as follows:
Joshua Hewitt born 1769 ?Prescot married to Ann Rimmer born 1769 ?Prescot on 10.8.1788 at Farnworth Chapel which is close by to Prescot and is the Chapel of ease to St Mary Prescot.
Joshua is a watchmaker
Also I spotted the possible witness of the aforesaid John and Ann marriage (Mary Hewitt born 1791? who I assume is his sister) living at The Angel Inn Eccleston Lane ends in 1841 age 50 living independant means. Very nearby in Lane Ends is Joshua Hewitt age 45 (b1796) A Watchmaker with Mary his wife, children John 5 and Ann 2 .....brother and sister of John maybe?
If you know Prescot you will know that The Angel Inn was on the opposite corner to the Wellington pub just where the WW monument is standing now and just opposite was Lane Ends Cottages
All of this is on Ancestry, if you cant find it PM me I have detail.
Hope this helps, but check it all anyway just to make sure