Hello, sorry I took a while getting back on this one. I couldn't find the specific people you were looking for, but I have included all the possible links to the surnames you mentioned, including middle names that may well indicate a mother's maiden name.
GWENNAP WESLEYAN CIRCUIT
PENBERTH Catherine Jane
7th Aug 1844
daughter of William and Catherine Penberth of Gwennap, was baptised aged 5 months by James Akerman.
ST IVES WESLEYAN CHAPEL
PENBERTHY Eliza Catharine
14th Feb 1836
daughter of John Penberthy of St Ives (Miner) and Eliza his wife, who was the daughter of Thomas and Catherine Bohanna. Born 8th Jan 1836 baptised by James Mowat
PENBERTHY Sarah Catharine
28th July 1836
daughter of Isaac Penberthy of Halsetown, St Ives (Miner) and Sarah his wife, who was the daughter of Thomas and Catharine Bohanna. Born 11th March 1836 and baptised by John Bond.
----My comment- looks like two brothers may have married two sisters here.
HAYLE COPPER HOUSE WESLEYAN CHAPEL
Josiah
10th Jan 1826
son of John Penberthy of Rosengrows and Amy his wife, born 18 Dec 1825 baptised by Thomas Webb
REDRUTH PRIMITIVE METHODIST CHAPEL
17 Aug 1834 George William Burn son of Henry Burn of Falmouth (Joiner) and his wife whose maiden name was
PENBERTH, was born 27 July 1834 in Falmouth and was baptised by John Richards.
----My comment- No christian name of mother is given
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I can't find a Stephen Penberthy, but I thought that these Penberth(s)/ies might be connected to your Stephen.
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POLGLAZE
Martha Weeks
Polglaze Goad
28th Sept 1828 Falmouth Wesleyan
daughter of William and Elizabeth Goad of Falmouth (Shoemaker), born 6th Sept 1828. Baptised by Thos. Martin.
John
Polglaze James
15th Sept 1792 Falmouth Wesleyan
son of John and Mary James of Helston. Baptised by J.B. Wildbore
Henry
Polglaze Trestrail
8th June 1817 Falmouth Wesleyan
son of Robert and Alice Trestrail of Falmouth (Cordwainer), born 3rd May 1817 and baptised by John Hawtrey.
John Austin
11th July 1837 Luxillian Bible Christian Circuit
son of William Austin of Tywardreath (Miner) and his wife, who was the daughter of John and Phillippa
Polglaze, born 16th March 1833 and was baptised at Tywardreath Chapel by William Courtice.
Mary Ann
Polglaze 6th Nov 1814 Ponsanooth Wesleyan Chapel
daughter of Joseph and Ann Polglaze of Falmouth (Mariner), born 24th Sept 1814, baptised by Fras Truscott.
Francis
Polglaze19th April 1820 Hayle Copper House Wesleyan
daughter of Ralph Polglaze of the parish of Deveral in Gwinear and Eleanor his wife, born 26th March 1820, baptised by W. Flint
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BURIALS
Francis
Polglaze of Falmouth aged 36 was buried 26th June 1827
by Edward Muscutt- Falmouth Independent
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NOTES-
PENBERTH and PENBERTHY might as well be taken as being variants of the same name- unless I am mistaken.
PENGLAZE is a Parish in Crowan.
POLGLAZE
I don't know much about this family but there seems to be a lot going on around Falmouth.
Hope that helps you, and maybe others!
;D