I do not see how it is possible for everyone on a 4 day cruise to get a seat at brunch since there is only one day that it is offered.
Breakfast will be served in BBB and I think that it will be in Triton's and possibly PC. Palo does not serve a breakfast. You go to breakfast whenever you wish when the dining rooms are opened. Lunch is the same way. Don't forget the food places on deck 9 are open most of the day too.
For Palo reservations the concierge guests and those who have reserved the REAS package get first pick at resies at 105 days before the cruise, return cruisers get to make resies at 90 days and first time cruisers make resies at 75 days. There should be enough seats on a four day for almost everyone to have a dinner resie but it may not be at the time you wished for. If you are flexible they will be able to put you on a wait list and call that afternoon if there is a cancellation. Also, the only put about 50% of the resies online. If you get to the port early you have a better chance of getting a resie at Palo if you didn't get one online. They do hold back some resies on boarding day for concierge guests who didn't book online and once they are given their choice that first day, any spots not taken are opened up to the rest of the guests.