You are all suffering and your grief isn’t selfish, especially when it’s about feeling for the suffering of your loved ones.. It will get easier slowly over time. If they are local, you might want to be practical, maybe take the gc out for food, specifically ask your daughter regularly, what you can do, maybe babysit if needed, cook, shop, spend time with them if that’s what they want. If far away, maybe short visits….there or close by. Know that children are so resilient …they will appreciate realising the family structure ( which includes you) will carry on. Be prepared for the long haul and take time for yourself too.