Good for you..one point to share, in the types of situations you should be prepared for many events. The baby may not live long enough for the photo shoot - so be prepared for that, the baby could go 'during' the photo shoot..your emotions will be all over the place..so will everyone else. We were fortunate to have the time when mother died to spend the day at hospice with her, the one thing wished I could have done was brought a camera to capture everyone coming and going throughout the day..but the family was not open to the idea and out of respect..you get the idea.
So since the family has approached you..please do it, you will be amazed at how you go into auto mode and how you will get through it...
Good Luck and Thanks for Sharing.