GEDCOM files are downloaded from the IGI (International Genealogy Index) maintained by the Mormon Family Search organisation.
These files are a list of birth, marriages and deaths obtained from the Wiltshire Records Office, and each one is individual, not linked to a family. For example, you may have a birth registered, and this would state the father, mother and the child. If that same couple had another child, that entry would be an individual record too. So there would be the parents listed twice. The trick here is to find all the children and merge them into one family group. This is often easier to look for the town and date in the first record and then scan for those parents in that town, in that period.
You will need a genealogy program to operate a GEDCOM file. On a MAC REUNION is an excellent program. Family Tree Maker works on a PC. There are many others, some even free of charge.
Surnames of CASWELL, TITT, BUCKERIDGE, WALLIS, and a few others can be found in the file at www.moonrakers.com/caswell.zip This is a large file of over 100,000 names, mostly linked.