This is difficult, because most of the sorts of recommendations I'd make hinge heavily on knowing something about the characters. It's really hard to stimulate RP between three blank slates.

Do any of the PCs have beliefs or attitudes or something that you can built a grey-area talking session around? What sort of "morality standards" are we talking here? "Is it okay to kill people who disagree with you?" "Rob from the rich to give to the poor?" "Do souls in the afterlife have rights?"

This whole question is kinda too broad to give satisfying answers to, I think.