Hi Sue
If this couple were married in Guernsey, then the marriage record may give more details, depending to some extent upon which church the marriage took place in.
There are no proper immigration records for Guernsey- there are some difficult to decipher arrival records for a short period in the 19th century but they don't contain much detail.
The best bet would be to contact the Priaulx library,
http://www.priaulxlibrary.co.uk/ who hold the vast majority of available records, and for a fee they will undertake a search for you. They will also be able to provide baptism records for the two children, and the death records, etc., for any of the family who died in Guernsey.
Good luck with the search!
Andy Smith.