My heart goes out to you.
Just remember tha people deal with pain differently, maybe the fact that they weren't there when he passed on is just a reflection of how they were dealing with their pain. Maybe they didn't feel strong enough to give him comfort.
You being with your mom is commendable, but ook at what it did to you.
So, just think that they did the best they could, maybe not what you would have done, but still, the best they could.