A son will always be a son,
But, you can lead a horse to water but you cant make it drink, if he cant accept the situation , doesn't help, doesn't speak and leads his own life no amount of you trying will change that, it is up to him to come too terms with it, As it has been for you. as a couple you are dealing with what life has dealt you, that is a lesson he has to learn for Himself, you have the support of your daughter, she has accepted and come too terms with it and is there for you and your husband as you are for her.
if you help him financially will buying his happiness change things?.
the 'guilt trip' was just to turn it back on to you, Make life as best as you can for you and your husband, when he has grown up and accepted it and made his own path in life things might change.