Dents in frame rails and cross members. Floor pans that have been crushed inward. How are they repaired?

as much as you may not want to hear this, the frame rails look like there may be rust issues, although how bad remains to be seen.
the only way to repair the dents and crushed areas is to cut them out and weld new material in there.
if the rails are too far gone, rail replacement will be required.
as to the floor area, a [REALLY] BFH and a piece of wood could possibly be used to get the floor into it's approximate position, depending on what your wanting the outcome to look like.
if the floor is rusty at it's edges, you may be in for a floor pan replacement.

Stud welder and slide hammer on the frame rails and blocks of wood and a big hammer on the floor pans. If the pans have any obvious dents lines or creases work those out first and the rest will want to spring back into shape a lot easier. You could also work on those frame rails upside down by welding some pull tabs or washers on the frame rails and pull them downward with a chain and a barbell weight attached to it to act like a slide hammer. When done you have to grind the tabs off and paint over it.

When rust is really dark colored and scaly on sheet metal then it's usually about to go thru, or has big pits hidden under it. Lighter colored rust, like what I see there, may look worse than it actually is once you clean it down to bare metal. I've cleaned up stuff that looked like that and found it to be a mix of dried dirt and rust with nice metal hidden under it.

Before assuming anything related to rust, I'd suggest using a scope-style camera tool inside the frame rails to see what they look like.

Agree
Could be distorted from rusted/weakened rails.
Or, someone placed a jack or stands wrong.
Tapping the areas with a small hammer may give some insight.
If light tapping produces more distortion, then likely rusted/thin.

Some sections look bad and some look OK. Thanks for all of the replies and providing me with some insight.....definitely need to take a harder look and do some "probing".