The back one doesn't look that bad in the picture although the ends look a little close to the paint. If it is twisted, you can tell by taking it off but keeping the brackets on. When set down, the brackets should both sit firmly on the ground without rocking. If there is a little twist you can put one bracket in a vice and gently twist the other bracket with a large wrench or other lever. You can also put shims between the brackets and cross member (high or low) to effect a change.
If you stand directly over the front of the car and look down at the bumper, it should be parallel to the header, both top and bottom edges. And obviously the grill edge should be parallel to the bottom edge of the header panel. I would take the bumper carefully off (lots of tape on the ends), remove the vertical bolt at the back end of the brackets if they're there and loosen the 1/2" bumper bolts enough that they can be moved a little and then slide the brackets out so the four ends are all equidistant from the header. You can then see if the bumper wants to fit in the correct position. At that point you should be able to tell if the shape of the bumper is wrong or that maybe the brackets are bent.
Good luck
