One of the stages of grief is anger, and it's easier for him to take it out on those closest to you, than strangers. We often take out our stresses on those closest to us (not condoning it, but it is true).
Grief is not rational. It is messy, complicated, unpredictable and confusing.
He probably doesn't know why he behaves the way he does.
He's probably angry at his dad for leaving him. Angry at himself for all the things he did/didn't say to his dad (and now never can).
He is probably also scared of being too close to you at the moment. When someone you love dies, it hurts, it hurts like crazy. It's logical, in a way, to distance yourself from others you love. He may think (wrongly) that in doing so he won't get hurt again.
He's probably also facing his own mortality. He's scared. His dad can die, and it brings it home that he can too, and that is a scary reality to face. Sure we all know it, but we know it in a detached way; your DH now has faced it in an involved way.
Grief though is a selfish journey. You can't do anything to hasten his arrival to the end of it. You can be there for him, hug him, let him know you love him & are there for him, but there is nothing you can say or do, to help him journey through it quicker.
When my second DD was born sleeping, I became detached from DD1 (who was 16 months old at the time). Partly I was scared of loving & being hurt. But I now realise that it was more due to my need to retreat, to work though my feelings. I couldn't be as emotionally available to her, as I needed a whole heap of my head/heart, to work through my loss. I never thought I'd recover the love/closeness, but I have. I'd even get angry when DD1 would wake in the night, as I wanted her sister, a newborn, to wake me up.
The guilt is the main cause of anger. But it is complicated.
Whilst I believe the above to be true, it's not fair for your DH to make you all feel rubbish. While he can't help how he feels, he can be made aware of how he's hurting you all.
Has he been referred for bereavment counselling? Would he go? It may help him to work through things, and be able to manage his feelings without hurting you (especially your DC) irreparably. Try googling CRUSE.
He may also be depressed (men aren't as good at expressing their feelings, and bottled up grief can easily cause depression), so it may be worth him seeing his GP. Antidepressants don't cure grief - there is no pill that can do that, but if he is depressed, it may help him get a handle on his feelings.