My great grandma died in the house I live in, and I'm in the room right above the room she died in. there's a walk in closet with an attic inside it. I've noticed that every time I leave my room (with the door closed) and I come back the door is wide open. I also hear things knocking on the inside of it. Also whenever I go in there I feel a slight breeze, but I always keep the attic door closed and sealed.

I could just be a simple case of the door being slightly off plumb and a weak latch and/or weak latch plate. The slight cool breeze could be leaks from your doors and/or windows. Check those things first.

Two things

It was your grandpa, so any ghost would not be a threat to you, merely watching over you.

Latch the doors shut better,