“ we are going to sit in the bleachers for the football game” is one way to use “in” but another way I personally use “in” would be telling someone directions to where I am such as, “I’m sitting in the bleachers. Can you see me?” Vs “Sit on the bleachers.” The word “on” can be more of a current action or demand, such as a mother telling a child to sit down on the bleachers. “On” is used more direct, I find. However, using both either way is completely fine. You can use it interchangeably. This is just how I see people using it. :)

Both work great. The word "bleachers" is both a place to sit 'in' and an object to sit 'on' (sometimes even 'under'). "I spent gym class sitting on the bleachers talking to my friends." "We took our seats in the bleachers right before the game started."

I agree with Erica, though I would probably use “in” personally.

Both can be used.

Hello Josie! The correct preposition is "in".