I'm sure John and Hastings will eventually need some sleep from dealing with their detectives all day. :-)

At the moment I've fudged a little by having Poirot and Sherlock arguing in French, so John and Hatings can't understand them, so I don't need to worry about them joining in the conversation. Also keeping both pairs across the room from each other so the other can't hear what they're saying. I'm also having Lestrade guide the convo a little by purposely asking what everyone thinks. One day they will all need to speak though, and on that day I will cry softly into my keyboard....