If you book a room with breakfast for 2, and if you'r also Plat+, then you get 4 breakfast each morning. At least that is how it has worked for me. FYI, but you may have to be very clear to the front desk agent that your room includes 2 breakfast and also that as a Plat+ you'r still entitled to 2 breakfast for a total of 4. This is how it worked out at Boston Sheraton in 2019. The rookie did not understand this but his manager did.

In NY, I've had the third person's breakfast comped out of the final folio, but that was managements decision, but going into the restaurant, I fully went in expecting to pay for the third person.

To OP's question, I've not had any lounge limit my group, which is usually 3 people including myself. Even at the Marriott Marquis San Francisco, which has someone up front during breakfast to keep out interlopers, no one questioned me bringing in 2 other people with me. The agent just thanked me for being a Titanium member and let me and my party in. What was more surprising was how many parties were turned away at the door for not being plat+.