Deb...sorry for your pain
My dad died when I was 28, it blew me away when I sobbed like a kid considering he was abusive and I had spent most of my life daydreaming of beating the crap out of him. It wasn't until I moved out that we started to have a somewhat normal relationship and now that was gone, seemed like we really only had a few years.
I figured out later most of my grief was because I felt jipped for never having something so many take for granted, a dad they're proud of. I even felt guilty for feeling that way, when I spread his ashes in the places I knew he loved to go not one of my 4 brothers showed up. Guess they remembered the bruises and the fear too. My sister and I talk about him and why he was the way he was but my brothers have pretty much surpressed everything.
If I were you and this will be difficult...talk to your x-husband, it may help him and them too if he initates a conversation in which he apolagizes for some of his past deeds and reafirms to them that he did love them a great deal. He may not even need to apolagize, just tell them he loves them and relive some of the special moments which were precious to both them and him. Memories which they can take with them after he's gone instead of guilt or hate.
Once again sorry for the pain you feel inside and the pain you feel for your children.