Hi Tony
I'd be inclined to have a closer look at the William EVANS licensed in 1835/died in 1852 before writing him off completely.
The 1851 Census has this household :-
131 Bedford Street, Toxteth Park, Liverpool
William EVANS, 37, widower, pilot, AGY Holyhead
Elizabeth, sister, U, 39, housekeeper, AGY Holyhead
Catherine, daughter, 10, LAN Liverpool
William Owen, son, 6, LAN Liverpool
Richard H, son, 2, LAN Liverpool
Elizabeth EVANS, servant, U, 22, CAE Caernarvon
And the 1841 Census this one :-
Edmund Street, Liverpool
William EVANS, 25, pilot, No (not born in Lancashire)
Margaret, 25, No
Catherine, 7 months, Yes
Lancashire BMD has this marriage
1839
Liverpool St David (the 'Welsh' church)
William EVANS and Margaret JONES
The Liverpool St David Parish Registers have these baptisms :-
4 December 1840
Catherine, daughter of William & Margaret EVANS, pilot, Edmund Street
23 September 1852 (born 19 September 1844)
William Owen, son of William & Margaret EVANS, pilot, Ray Street
Somewhat perplexingly, there's also this baptism :-
17 January 1847
Liverpool St Paul
William Owen, son of William & Margaret EVANS, pilot, Ray Street
It looks as though pilot William EVANS' wife Margaret died not long before the 1851 Census - possibly whilst (or shortly after) giving birth to your 2 x great-grandmother named after her.
The Pilot Character Book in the Merseyside Maritime Museum Archives should list all the children of the above William EVANS, pilot, who died in 1852. If the list includes a Margaret as well as a Catherine, William Owen and Richard Henry, then this William EVANS will almost certainly be your 3 x great-grandfather.