It is simple, 2 pax can enjoy the diamond benefits per room, anything beyond that is a gift.

Now I have had instances where I booked 2 rooms for. 2 pax per room and confirmed ahead if the 2 pax of the other room would be granted the same benefit, usually they are as the hotel wants the business, I contact the hotels before booking, but some are stickers for the rules. I also have had breakfast charges for the second room after I agreed before booking it would be free, that was obviously effectively dealt with.

Globalist