Sarnia
I worked on a Delivery Suite for 17 years and one of my jobs was to work as the Bereavement midwife's assistant making sure all the paperwork was available and up-to-date. I am assuming you are in the UK. If you are there is a brilliant organisation called SANDS (Stillborn and Neonatal Death Society). On discharge your daughter should have been given details about them. There are leaflets for grandparents, other children, work colleagues etc. Of course, reading leaflets is the last thing the parents want to do when faced with the heartbreak of losing their baby but in time and it has to be their time, the day may come when they want to reach out for SANDS and meet others who have experienced the same torment. You could Google them for help for yourself. They are a nationwide organisation and very experienced inn helping bereaved families. I am so sorry for you all. 
SANDS has a garden at the National Aboretum in Staffordshire too. Yes, they can be very supportive of parents or any other relatives who feel the need for their help.
I am so very sorry for your loss, Mandy45
Your daughter and son-in-law may seek your help in the coming weeks, it must be so difficult for them and for you too at the present time.