I stayed earlier this week and was pleased to find no upcharge for Diamonds enjoying a full breakfast in the restaurant, now that the Ambassador Lounge is closed for breakfast Monday to Saturday.
Here is the information flyer provided to those with Ambassador Lounge access. The $39 charge for additional guests enjoying breakfast with you in the lounge is ludicrous considering it's about 1/5 or 1/6 the quantity of what you get in the restaurant for exactly the same price.