On the Dream, you will have Palo and Remy's. You can book a dinner at each. In addition, you can book brunch and tea at Palo.
You are probably aware that Palo brunch and dinner have a $20 per person surcharge, tea (I believe) is still $10. Remy's is $75 per person.
Not all reservations are available on line; if you cannot get what you want on line, you will have a chance to book after boarding. If the issue is one of date/time, book what is available on line and change it after boarding. It is easier to alter a reservation than to make a new one (at least sometimes!)