Is there anything I can do to calm my daughter down over the death of her son?

Just being there for your daughter and son in law can help. Try to be sensitive about their loss when your baby comes. Still give them a lot of attention. They are going to need it. Allow them to heal. Im so very sorry for the terrible loss, im sure it has been overwhelming. Try your hardest to move on, and let go of the saddness and gain joy from your own children. Your daughter is not going to think of him as her own son, but she may resent him a bit. out of jealousy. and she may resent you as well. Still be sensitive, do not blame her for her pain. She's trying to work through it.