STUDENT: I think conjoined twins can be good or bad.
CORRECT

STUDENT: First bad thing is when they go to the toilet they might be very uncomfortable
CORRECTION: First, the bad thing is when they go to the toilet, they might be very uncomfortable.

STUDENT: Good thing is when they needs to test they can shar their brain.
CORRECTION: The good thing is, when they need to take a test, they can share their knowledge.