Janice
Elizabeth Perry d. of Mary - aged 25 as given in the 1851 census - was born in Chippenham WIL.
If you go to
http://freepages.genealogy.rootsweb.com/~hughwallis/IGIBatch... and search the first Chippenham batch given you will find Elizabeth Perry bap. 30 Nov, 1823 parents William and Mary. I'm not saying that's her but there's every possibility it is - extracted data are very reliable regarding extraction accuracy in the main.
You'll find the hugh Wallis site useful and it might be an idea to get the free programme Parloc (parish locator) from
http://parloc.pwp.blueyonder.co.uk/parlocdl.html it too is very useful.
There is no sign of Benjamin, John or Eliza anywhere that I can find and although John was said to be born in Nailsworth, the LDS have not extracted the data from its parish records so another film needs searching!
I spent a fair time looking but could not find any of the family for certain in the 1841 census.
Regards
Geoff