They choose to sit down at the stool where there's no plate. And yes, there is room to sit otherwise.

Don't worry. As long as they are at the table while the plates of food are there, their hunger is being appeased. Check they're details after they leave the table.

Yes, that's the "studying in the kitchen" seat, so there is never a plate there. However, they must be doing a fine job with the boarding house reach whenever a person sits there for a meal because they get full just like those sitting anywhere else.