Preflop: Limping is OK
Flop: I would reraise MP1's raise. Two players had already checked, the only made hand that makes any sense in checking is Axd, and even in that case I would bet it. So by the time the action got to you - check, check, bet by MP there is a decent chance you have the best hand - the one thing you dont want is a 4th diamond hitting, so reraise the flop.

As played the CR by BB is very troubling, I would call and hoep the board pairs