I agree w/Ginger. I would do a trial run w/his request and if you discover that the children aren't getting their homework done or not focusing in school, then suggest an alternative date for them to stay over, i.e., maybe a Friday or Saturday night.
He is their father and I don't see where his request is all that terrible right now. At least he wants to spend more time w/the kids and most of the crisis people don't want to do that.
Separate yourself from the scenario and step back a bit. This could be a good thing...but you need to try it out first and see how it goes. If it works, continue doing it, if it doesn't, well, suggest an alternate date.
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.
