My floor is sagging and very bouncy in some spots.

I am looking for some advice on what I should do, I have a few spots in my floor that sag and bounce when you walk over them. It has caused some cracks where the walls meet the ceiling. I am wondering if I should call a contractor, install joist jacks or just glue and nail (sister?) in some boards on either side of the joists. The latter was done in a few spots by the previous owner, but not very well.

Its a real pain in the ass as you can feel them move when someone walks by the couch or when you walk by the fridge it kinda moves.

Link to some pictures from my crawl space and the ceiling cracks. Note that the joists have no support other then at each end and stretch about 23 feet.

Here is a video

Has anyone else dealt with this? Any advise you can offer would be really helpful in figuring out what I should do.