Just some random thoughts - I hope that they help you Alison.
I think you have you depersonalise this as much as you can. Don't see your husband as your husband any more see him as an object same with OW. Force yourself not to think about them as people.
As for your children you husband isn't giving them any choices. None at all. That means that you have to give them all of the choices. So, if they want to live with your husband you have to let them and then support them in their decision. If they want to live with you then so be it. But it's not a popularity contest. This is about your children and their lives.
Same with the photographs. If they don't want to have their photograph taken it's sad and all but they don't want their photograph taken. That's life. But it's not the end of the world.
Speaking personally I know that if I'm not allowed to make my own choices I become quite random and then make silly choices. If I'm allowed freedom and space to decide I seem to make better choices.
