Am sure you have now found all this information as your posting was a few years ago, but I have just started on the Mallett line, it is a distant ancestor.I found the following about your line:-
Alfred Mallett -Christening:14 FEB 1830Cambridge,Slimbridge,Gloucestershire, , Gloucester, England Death:18 APR 1878Fermain, Saint Peter Port, Guernsey, Channel Islands.
Which would tie in with your Alfred Daniel Mallett being born in Guernsey.
Based on his father James Malletts birth date given in 1851 of 1795 then I would think that this is James's christening Christening:26 DEC 1793 Slimbridge, Gloucester, England.This would make his parents James Mallett and Mary. I found the marriage listed under Slimbridge as James Mallet & Mary Cowly 13 Oct. 1789
I believe I found their deaths in the burial index...
23 Sep 1819 James MALLETT 56 Gloucs Slimbridge, St John the Evangelist 14 May 1828 Mary MALLETT 70 Gloucs Slimbridge, St John the Evangelist
I can probably find more information but want to check this email address and enquiry are still active.Best wishes, Claire