I have had a look at Huntingdon Archives and found some answers and some more questions for you.
If you find you get a lot of people from St Ives then the records are transcribed and available on fiche or CD
http://www.huntsfhs.org.uk/cgi-bin/hfhsbookstall.cgi
Baptisms5 June 1805 William Smith son of Thomas and Anne. Born 18 April 1805.
6 Sept 1807 James Smith son of Thomas and Anne (2nd Reg his wife). Born 13 June 1807. (brother to William)
19 August 1810 Sarah Newman daughter of Thomas and Anne (alias Smith). born 31 July 1810. Probable sister to William and James. See the parents marriage for the alias name.
13 October 1812 Elizabeth Richardson daughter of Anne. born 23 sept 1812 illegitimate (2nd Reg natural)
12 July 1780 Thomas Smith son of Ann. Born 19 June 1780. Possible baptism of William's father
22 Oct 1794 Ann Richardson daughter of William and Esther. Possible baptism of Elizabeth's mother
Marriages17 April 1804 Thomas Smith (alias Newman) bac otp and Anne Lovell sp otp by Banns. Witnesses James Smith John Siphell and Jacob stevens
20 Feb 1829 William Smith bac otp and Elizabeth Richardson sp otp by Banns. Witnesses Charles Stevens and John Maile
28 March 1787 William Richardson bac otp and Hester Barr sp otp by Banns. Witnesses John Newman and John Bennett
Notes1. Between 1803 and 1813 there is a duplicate register. Any differences to and in this register are marked (2nd Reg)).
2. Around 1780 (1777-1802) there is a Thomas Smith and wife Anne vicar at St Ives. I do not know if there is any connection to the Thomas Smith father of William.
3. Anne Lovell was not baptised in St Ives as far as I can see
4. I could not attribute a burial for William or Thomas Smith in St Ives 1841-1851