Tim,
sorry I've not checked in for a while - sounds like things are extra weird for both of us.

I'm with broke's thoughts on this. I would think that if S13 gets counseling, then I'm not sure why the WW would think that them reaching out to his brother would have anything to do with you. Especially if you talk with them about it ahead of time. The excuse could be S13 said something that caused them to want to talk with S16, just to check in with him at the very least. They are siblings - so what is causing issues for one could certainly be of concern for the other.

Good luck and do check in once you learn something.

Me: 58
Her: 59
Kids: 0
Dog: 1
ILYBINILWY: 9/15
D Bomb: 1/11/16 (found out filed)
Verified OM: 1/11/16
Moved out: 1/11/16 (thought it was temporary)