If they are in the same room as you, then everyone must be on the plan.
If they are in a separate room, then yes, you can add the dining plan to their room and not yours.
In otherwords, if you are in a studio and they are in a studio, yes, you can get the
DDP for them and not for you. If you are all in a two bedroom unit together (even if it is a lockoff), then no, it is everyone or no one.