According to the link, the classes would stay to their designated areas but can visit if they change clothes or something like that
The Titanic II has kept various features based on the class system of the early 1900s. Like the first ship, it will have a gym, Turkish baths, a squash court, a grand staircase and swimming pools. It will also retain the dining rooms for second and third class, as well as Captain Smith's sitting room, bedroom and quarters. Passengers will also be given 1920s-area costumes, which will be included in state rooms upon arrival and will be a part of the ticket fee, to help recreate the experience. First class passengers will not be able to mingle with those in second or third class, but will be able to spend a few days in different quarters, which will require people to change clothing.
This post was edited on 2/26 at 9:47 pm