There are loads of Hills on freereg especially in High Hams so do have a look and plough through them, here are just a few
William & Charity Hill - can't see any marriage for this couple yet
Charity wife of William Hill buried 1 Nov 1747 High Ham
William buried High Ham 6 Jul 1763
Children of William & Charity are as you have listed except James was baptised 24 Feb 1734 High Ham and as mentioned before the burial date for John seems to relate to the base born son of Unity Hill. William 1741 married Martha Wallis High Ham 24 Apr 1770 (Martha buried High Ham 8 Dec 1785). Tobias 1743 buried High Ham 8 Mar 1789 - in old age, can't find a marriage for this Tobias and an Elizabeth/Betty but Elizabeth possibly buried High Ham 25 Feb 1787
George Hill b1737 parents William & Charity, died 1813 married Rachel Moon 3 May 1753 High Ham
Children bap High Ham
Charity 16 Oct 1757
William 20 Jul 1760
Grace 28 Oct 1764
George 20 Apr 1766 married Sarah Lawrence Moorlinch Oct 1788, children bap High Ham :-
William 2 Jan 1791
Joseph 31 May 1795
Can't see an obvious burial for either George or Sarah in High Ham so presumably they moved to a different parish (maybe had more children?)
No other details such as occupations etc shown for those records above, not unusual in the early years
Also look at
www.genuki.org.uk , if you check out High Ham and click on nearby places you can check other parishes, myweb.tiscali.co.uk/ian.sage/PR/pr_index.html shows you what is online for Somerset parishes
Good luck with your research
Shirl