Answer:
What has many keys but can't open a single lock?
I fill a room but take no space.
I'm an old relative who's hand's can't hold anything and eyes canβt see anything
With three eyes and as black as night I frequently knock down ten men with a single strike!
I am a protector. I sit on a bridge. One person can see right through me while others wonder what I hide.
It has no top or bottom, but it can hold flesh, bones, and blood all at the same time.