I don't really have any advice. I just wanted to let you know I'll keep you and your husband in my prayers and to let you know I know what you're both going through.
It's really hard losing a parent. I lost my Dad 3 years ago very unexpectedly of a massive heart attack (age 61). Until you've lost a parent, it's hard to realize what it's like. The shock, the anger, the fear, the pain, the madness. Then my FIL passed away very unexpectedly 1 year ago from a stroke. It's so hard. I never realized how hard it is.
I did read a few books from the library on death and dying. A book might help your husband if he's the type that doesn't want to talk about it. I do not like to talk about it to strangers or people other than very close friends. Otherwise, it's too hard for me. So getting a few books might help him ease through the pain and also to reconfirm that what he is experiencing is totally normal and it will get easier.
Talking about it does help too (with the right person, if he's comfortable with it). Talking about what a great person he was, and finding special ways to honor him might help. I always buy plants for my Dad to take to the cemetary and whatever I buy for him, I but an identical one for me to plant in my yard. Then, every day when I walk through the yard, I look at the plant/flower, I think of my Dad and he's always right there with me. I know it sounds silly but it's little things like that that help me. I still cry from time to time and it's been 3 years so just know that the pain does get easier, but it's still very hard. I believe people who don't talk about people who have passed away are in denial. There are people in my family that every time I say something about my Dad they just stare and me and cringe. Some people are very uncomfortable about death and once someone is gone, they fear mentioning their name. Don't be afraid to talk about him or comment about how he would have really liked something or how he would have really found something funny, or whatever it is. Don't be afraid to have pictures of him in your house, etc. I still have photos of my Dad. To me it's a way of honoring him and still having him in my life, even though he's really gone.
I'm sure that one thing your husband feels upset about is that your dear child will never know his Dad (his grandpa) That has been very difficult for both my husband and myself, that our Dad's are not here to share in our joy and experience our kids. We just try to be thankful for every day we did have with them.
Anyway, good luck to you and your husband. After you lose someone very dear to you like a parent, it totally changes you as a person, or it has changed me.