Heartbreaking for you and your babies, I'm sure and I think the picture in the room are a nice idea. But honestly, you can't shield your children from life. Their Mom may love them and it's important that they hear that and know that, but going out of your way to keep her in their lives could potentially end up causing them more harm then good if she decides not to live up to whatever hopes you have of her.
I would engage her as she is willing and leave it at that. If she wants to be more involved then assist her in that process, but don't push something that isn't there.
Just my two cents.