This looks like it was baked "out of" somewhere, rather than the actual (correctly rigged) file. The only thing I can think of, for you to work, would be to arm (create) a basic rig, and apply constraints to those bones to the bones on your given rig.
The second thing you need to do is to "bake" in Blender, each action from each of those bones. That means, you'll delete everything but "walk" from the outliner (save an "original bones with mixed actions" files first), then save the "walk" file. Clean and delete everything that is not "walk", save "walk" file". Do the same for the remaining actions.
Open the "walk" (action only) file and do a BAKE to YOUR basic rig. Delete your given "walk" actions and the previous (broken) rig.
Now you have a completely re-build Walk (baked) action in your new basic Rig.
Go to your ACTION EDITOR WINDOW and NAME the action accordingly (this is important, so you can pick it up, later).
Do the same for all other files.
When you complete all that, you can go to your "walk" (baked) action, and FILE>Append>yourOtherBakedSeparatedActionFile.blend>ACTIONS>Append.
You will now see it on your ACTION EDITOR (name that you given your action from the previously fixed files in their action editor window).
You can now push this action into the NLA, to be exported (file>export>fbx> Press N > export NLA clips and Actions) when you're done editing them.
After all of this, you can now start EDITING whatever you needed to edit.
Here's an in-depth video about what gets exported and what not (from other applications into Blender), this is a recommended watch since you inherited a non-editable file, thus you need to reconstruct it, bake it, organize the actions so you can do your work.