A very precious baby - Yes, I know most babies are precious, but with a history of miscarriage and then going through the whole trauma of IVF, this is very special.
Obviously, your DiL is going to be intense and nervous. With my first baby, I was totally convinced he was deaf and even got him referred at a few weeks old to a specialist. Nothing of the sort, just me being totally neurotic.
The best way of helping is to ask what jobs around the house you can do, ironing, meal planning/preparing, shopping, window cleaning, grass cutting. Let the new parents just enjoy these first magical months with their first, previous baby.
Congrats on being g.parents, just enjoy it.