what are we supposed to say again when christians ask us where we get our morality?

[Neo-Scholastic]

Are behavioral dispositions moral because they evolved or did they evolve because they are moral?

Better to say that prosocial behavioral dispositions evolved because they had survival value. Does that make them moral? No. Does it underpin what we describe as moral. Most likely. Morality is more like beauty than it is like reality. There is no objective basis for morality.

Perhaps. Morality has practical applications that extend into personal and public life much differently than aesthetics. It sounds like you put morality in the category of preference rather than proprietary. If so then the concept of justice has no foundation and I hate to say this because I know it peeves you but that's moral nihilism.