I have more than one kid at the same Resident camp but they are in separate grade programs, will they get to interact at all throughout the program?

Yes!   While they will have their independent experiences and won't be in the same activity group (and everything that goes with that), there is plenty of time for interaction at meals, evening activities, clubs, and any other all camp activity or transition.  It's great to know that siblings are on camp and to encourage them to support each other through their own adventures.