OK - this 1683/4 Dewens is a new one but I need you to 'confirm' that this was a burial?
If so then it took them another 20 years before using that name again!
As for the Andrew buried in 1708 - My understanding is that this was the son of Charles and Mary who was baptised at Lelant in 1686.
The year he was buried another son of the same name was baptised at Towednack and, according to John Tyack, was buried the same day.
There seem to be a few anomalies here so I will give you a brief outline of my current understanding of the family of Charles and Mary. (There may be a couple of notes attached here also) :-
Dewens - bur. Lelant Feb 7th, 1683 (KW)
William - bp. Lelant Oct 31st, 1684 - bu. Lelant Nov 21st, 1733.
(Married Jane GILES at Lelant Jan 1st, 1724) *** SEE NOTES
Andrew - bp. Lelant Nov 14th, 1686 - bu. St Ives Apr 18th, 1708
(bp. dates from IGI and also John Tyack )
Wellenett - bp. Lelant Feb 2nd, 1686 (IGI/John Tyack) - bu. 1688 (John Tyack)
Wilmot - bp. St Ives Feb 4th, 1689 (IGI) m. Edward Banfield 1719
James - bp. Towednack Nov 2nd, 1690 (Hoblyn) - bu. Lelant Oct 18th, 1733 (John Tyack)
(m. Mary Richards at Lelant 1721)
Charles - bp. St Ives Feb 19th, 1693 (IGI)
(m. Mary Cock at Lelant 1721)
John - bp. Towednack Apr 28th, 1695 - d. c.Aug 1738 (John Tyack) ** SEE NOTES
Edward - bp. Towednack Feb 13th 1697 (Hoblyn) - bu. Lelant Jun 2nd, 1747 (John Tyack)
(m. Margaret
? bef. 1735) ** SEE NOTES
Mary - bp. Towednack Nov 22nd, 1702 - bu. Towednack Apr 9th, 1705 (both Hoblyn)
Duence - bp. Towednack Oct 8th, 1704 (Hoblyn)
(m. Benjamin Richards at Lelant 1719)
Mary - bn. c. 1706/7 - d. aft. Nov 1752
(m. James Trewhela at Towednack in 1728)
Andrew - bp. Towednack Oct 31 1708 (Hoblyn and B.T.'s) - bu. Towednack Oct 31, 1708 (John Tyack)
** NOTES **
William - His Will was written October 29th 1734 and proved at Helston May 13th 1736.
But this shows him writing his Will AFTER he died!
BUT his brother James, in his 1733 Will, names brothers William and John 'of Helston'.
John - named as a 'dyer, of Helston' in his brother's Will and supposedly buried about August 1738 according to John Tyack.
Edward - I have a note suggesting Edward 'may' have been married twice.
Some sources link his son John t a mother named Elizabeth and, if so, then daughter Mary would also be daughter of Elizabeth.
If there were two marriages then son William may belong to either one.
Daughter Margaret was baptised as daughter of Edward and Margaret and this may be where an error has occurred.
Edward's son John named a daughter Margaret but - after mother or sister?
BUT - Margaret Tyack, widow, was buried at Towednack in 1796!
Leaving it back with you for now! ;D