SHOULD still give the fathers name, even if he is deceased. Sometimes it will specify "deceased", sometimes, if the person was not specifically asked, it may not, even if the father is dead.
(The possible I found in 1881 who was with widwoed mum - her name wasnt Sophia - so I think that it is a different one. But as I say, one step at a time - If you are sure that is the right marriage - ie if the children's births say mothers maiden name is Riches, then the marriage cert is the way to go. Otherwise, step back a generation to establish the correct marriage first)