Try getting the marriage certificate for Edward & Margaret and/or birth certificates of one or more of the children

The registry web site is: http://www.gov.im/registries/general/civilregistry/welcome.xml

Try www.familysearch.org

John & Mary were married in 1856. If they were the parents of your Edward, his name was William Edward and you may have to look under both names.
This would agree with his own son.

At census time, numbered forms were delivered to each household. The enumerator then copied these schedules into the census books.

Any excuse to visit the Island, but really, most of your basic research can be done by mail or on line.