Bedroom tax; sister in law in same house

I had an appointment for a DHP for bedroom tax.
DWP paying as couple but client claims it is his sister in law and they have seperate rooms.
I could appeal DWP decision but they do share household bills etc.

Anything to allow this in bedroom tax legislation?

Thanks Tony
I have been successful in previous DWP LT appeals but this is pretty unusual.
The brother in law is being paid as a couple after several interviews with DWP.

I will await his take on the situation before deciding what is the best course of action.

Is she named as his partner on his claim for HB?

no idea Sean; only met the sister in law this morning for DHP due to bedroom tax..

only 15minute slot so no time to go into situation at length.