Roscoe has been courting Bitsy the last few days. Yesterday he was very attentive to the empty nest box and both of them were going in and out of it. So I took the nestbox down to discourage them. But it did not work. Today I heard them mating. Their babies are not weaned and this would be their third clutch for the year. I am not sure what to do.

It takes a few days for hormone levels to go down so there could be a delayed reaction to the loss of the nestbox. You could try a very light application of the long nights treatment to help discourage them. Make the apparent night length a little bit longer than what they're used to right now. It doesn't have to be more than 12 hours, just it enough to make it seem like the days are getting shorter. Don't be too severe with this - you don't want their hormone levels to go down so much that they stop feeding the babies.

So from the couple times they mated yesterday she won't lay? He was a little better today.

It usually takes more than that. Since this is a third clutch they won't feel as motivated as they did with earlier clutches. So if she does lay an egg you can probably get away with removing it.