Well Damo - it seems, on re-reading your first post, that your first 'brickwalls' may be the identities of Thomas COWLING and Grace WILLIAMS.
That being the case then I have 'just a few' updates for you.
Grace Wall WILLIAMS bp. 22nd October 1819 at St Ives - 'bastard of Ann WILLIAMS'
She is recorded as Grace Hall Williams but this is undoubtedly her.
Grace died in 1883 at the age of 63.
Ann WILLIAMS will be just a tad harder to trace back.
BUT - I can do a little bit better with Thomas COWLING!
Thomas COWLING bp. 3rd October 1823 at St Ives 'bastard of Catherine COWLING'
Cathrine was bp. 2nd March 1794 at St Ives d/o Robert and Ann COWLING.
Robert COWLING married Ann REES at St Ives 29th May 1783.
I do not yet know when Ann died but Robert re-married to the widowed Prudence HUSBAND at St Ives in 1801.
Robert COWLING was buried at St Ives 24th June 1825 at the age of 66.
Now, as far as I can tell this will be Robert:-
Robert COWLING bp. 4th March 1759 at Tintagel
Parents:-
Thomas COWLING married Elizabeth FORD at Tintagel 26th August 1751
I cannot absolutely guarantee this last but I can find no other possible candidates.
It does look very likely however as COWLING does not appear to have been a name much in use in West Corwall at that time.
Now let me move forward again to Robert and Ann.
They had six children all born at St Ives amongst which was another daughter who had an illegitimate child - but I can fill in all those details for you later as your main interest at the moment I think will be to do with Catherine.
Sophia Reece COWLING bp. 5th December 1821 ' bastard of Ann COWLING'
But just before I go into that - your William (1854) was William Sisley COWLING and that is a name that now features most importantly for you.
The two daughters of Robert COWLING who had illegitimate children were both married at St Ives.
Richard SALTHOUSE m. Ann Rees COWLING 5th January 1824
William SISLEY m. Catherine COWLING 6th June 1825
In the 1851 Census at St Ives:-
Beach
William CISLEY, head, mar, 48, labourer, St Ives
Catherine do., wife, mar, 56, St Ives
John do., son, unm, 2, labourer, St Ives
Elizabeth do., daur, 17, dressmaker, St Ives
Ann SALTHOUSE, niece, unm, 25, St Ives
Thomas R COWLING, nephew, 7, scholar, St Ives
Thomas R COWLING, whilst recorded as a 'nephew' to William CISLEY, was actually the grandson of Catherine.
That should keep you going for a little while
so I will close in a moment and make some more adjustments/updates to my database so that I might be prepared for your next query.
But a couple of final comments before I do so.
It seems probable that one or more of the sons of Robert and Ann COWLING married given the burial at St Ives in 1819 of Robert COWLING at the age of 18 months.
There were two girls baptised as Grace Wall COWLING.
One was the daughter of Thomas and Grace and was married firstly to John Rouncefield BASSETT and secondy to Peter Husband BERRYMAN.
(This brings Cornishmaid into the discussion given John BASSETT's mother was Jane NOALL.) ;D
The second was the grandaughter of Thomas and Grace and was the daughter of their son Richard.
And this is another interesting point that may (or may not
) help with some identifications.
Although recorded as 'Richard' at Birth he married as 'Richard Eddy COWLING'.
What is most interesting here is that a Richard EDDY was a witness to the marriage of Thomas and Grace.
So could it be that he was the father of Grace???
OK - that should do for now - enjoy.