If I were in your shoes, I would wait to see what he has to say in his letter. I wouldn't write to him first. Besides, everything has been said that requires addressing....right?
If I were him, I would be putting forth the effort to write to my daughters. But, it's evident, he's still got a lot of issues to resolve before he can reconnect w/them as a parent or even a man.
Don't write to him...make him come to you first.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.