Hiya OP :-)
I think if DP is coming into DS's life and plans on living with you, then his plans should included being a stepparent to DS, and that includes all you listed about the bed bath routines and taking over some of your role when your in hospital with the new baby. Not unreasonable at all to expect this of him.
Perhaps he could move in sooner rather then later to get the hang of DS and being a step parent before new baby arrives?
~Isla Rohmaine arriving sept 2013 and a baby makes 3!