There are not a lot of irish records for the early 1800's.
Most documents such as census were destroyed in the Four Ccurts Fire 1922
Tithe Applotments 1823-1837 is the earliest census substitute www,genealogy.nationalarchives.ie
Griffith Valuation 1847-1864 www.askaboutireland.ie
(these would be those left behind)date for Fermanagh 1862
ps in my husbands history of the ship to Canada is that
two brother's travelled and one died and buried at sea.
I've been through Thousands of passenger ship records but
have yet to find any documentation to support that.
There were 5 Hewitt's with land holdings and 202 Wilson's.
The Parish's they had in common are Derry Vullan, Kinawley
Baptism records are available on line for Fermanagh with a not for profit but fee paying website. www.rootsireland.ie
& a free to viewwww.emeraldancestry.com
The Parish records except for one Parish RC 1783-1790 gap
1821-1900 and remainder 1810+ Cof I 1801 earliest Parish then 1836 & 1875 so as you can see records would be spotty
at best. With both parents names you should easily find any children they may have had in Ireland.
The British phone book for Fermanagh shows only 1 Hewitt listed and he is in Enniskillen, Fermanagh. 38 Wilsons with many in Enniskillen. You could try writing the Hewitt, the address comes with a postal code for Northern Ireland.