and can see that those are not joists going left-to-right in the ceiling, but what looks like 2x4s with plywood attached to them.
I’m thinking of attaching 2 new 2x4s to the 2x4s in the ceiling -- perpendicular to the existing ones, on both sides of the hallway.
Each new 2x4 will be attached to 3 existing ones with 4” lag screws.
Then will mount the pull up bar to these new 2x4s. The hallway is 51" wide and the bar is 50" wide, so new 2x4s will go right against the walls. The bar won’t need to support more than 300lb.