You're booking 2 rooms with 3 people, and the Titanium member benefits apply to one of those rooms, unless I'm wrong? You can ask for extra benefits either now or at checkin but they are not obliged to give it to you. Of course some people successfully bully hotels into giving them free things as well.
Don't know how a buffet at another hotel can be compared to the full day lounge at the hotel, including breakfast, evening food and the all day options. And of course the lounge itself which is really nice. I seem to remember that members (+1) are also given a choice of breakfast at the restaurant at the hotel, but not sure if this is still true?