We should be able to keep Moses, in fact I'd say it is not even a question that he should be allowed to leave, as we should be paying him what he wants, he knows we're virtually f**ked without him. But Moses also probably knows that there is a price point where if he stays, then other decent players have to leave, and I don't think Moses will want to stay if the team is not as good.
I can't see Brown leaving, but he needs to make a decision, as someone will offer to pay him more to play somewhere else.