I would tell him the kids are safe and they will be available for a visit on the agreed on day.. beyond that he has NO SAY in where you are or they are...

NOW the field is EVEN.. you don't know where HE is..and HE does not know where YOU ARE... lets see how he likes that?

It should make him panic and will most likley cause him to fight with OW since you aren't available to poke at...

You see, he will pick a fight with HER if you aren't around to offer one... So I say let her take the abuse instead... Right now she likley does NOT NEED that at ALL