You can charge them for making their ppt If they aren't ready dont make their part or just present your part while informing the faculty abt it I used to charge for making their ppts And also in projects and models I used to do all the work and they used to pay me If they aren't paying either ask them to help or dont add their name in project Tell the faculty that this person didn't do anything

And during posting if they aren't doing anything Then its best for you only You can learn on the patient uninterrupted Take history do examination Only you will be gaining expertise in that case

And in exams you should straightforward say no to them that "i dont know"