The two cops charged with assault but not the death are going to be acquitted, full-stop. Those are some weak charges. I could even see them being dismissed early on by an impartial judge.
I think the other four stand a good chance of being convicted, though. The murder charge is going to be very hard to prove, but manslaughter has a good case for it.
I guess Maryland doesn't have a felony murder law. The assault the officers committed/were accomplices to resulted in the unlawful death of Freddie Gray. That's the definition of felony murder.