When any of my DH family member's have past, I have just been there for him, and listened to the family speak about the person etc.

The only thing I really did behind their backs was organised a sporting team he loved to meet up with his brother. They were all so appreciative I did this. Other then this, like I said, I was there just emotionally for them

Maybe you could ask if there is anything they would like you to do or organise, and just be there for them. And especially your DH.

Sorry, you, your DH and his family are going threw this hard time.