The girls are split into an early and a late group. The members of the early group will eat/stay for a random time. If the place is occupied, the member of the late group using the same seat cannot join.Cool! Right now, I believe Jessica and Natasha always sit at far right. One time Jessica left and Natasha arrived to take the same spot. Depending on who is on the island, I am guessing it will not be possible for certain girls to be dining at the same time. Not a bad thing. Just interesting trivia.
So yes, girls using the same spot can never be together at the restaurant.
The reason is the number of necessary renders and very complicated code to do it differently.