FreeREG, I am still using the old site, has those Baptisms also, under THEIR;
All Saints, Huntspill
WILLIAM, 1 June 1794, THOMAS Baptised same day to Jno/Elizabeth (does not say Twins)
ROBERT, 09 Apr 1797
SARAH, 14 Oct 1798
ANN, 15 Nov 1801
JOSEPH, 30 Nov 1806
ELIZABETH, 9 April 1809
JAMES, 16 Aug 1812
All but William/Thomas have Parents as John/Elizabeth
Trish

EDIT;
This may be the Marriage;
7 January 1789, St Peter, Bleadon, John THEIR to Betty HANDY
They Baptise;
JOHN Thayer?, 24 June 1789, St Peter, Bleadon
So may have moved to Huntspill before William/Thomas were Baptised.