If you are happy for them to stay, put netting over your fish pond and dig them a small, shallow one in a corner of the garden if you have room. And they do love fresh water in it now and again, even ducks like to 'have a bath' and keep clean!!
I have 2 pet ducks and a couple of bantams and buy 'mixed corn' which suits them all. Most pet shops sell this in small bags starting about 2 pounds. One tip, any food you put out for them, put as close to the house as they are happy to come. If it's in a quiet part of the garden, everything else will eat it - crows, mice etc.!!
Good luck and enjoy them!!
Peeps x