I have a 1998 Jeep Cherokee 4L auto, when i got it, all the wheel arches and trim were in the boot, looking at the many parts, i can not work out how they go on.
Most of the bolts were broken so i have grinded them down so i can drill holes for new bolts, but i can not see any logical way for them to go on the jeep, especially the rear valance bit that goes up to the bumper as there is no way you can do up the nuts as it is a box section that has no access?

Here are some pics of my jigsaw puzzle......

 

Personally I'd keep them off IMO , I ripped mine out when I lifted her

 

Rivets for the rear part. That's how they did it from the factory.

 

The curved brackets fit over the lips of the flares to wedge them between the brackets and the body. If you have a welder or someone that does you can remove the old broken bolts and weld on some new bolts.

As for the straight brackets, they mount to the body for the plastic trim. I don't have any experience with their mounting as i have an older xj.

 

There are letters on them to tell you where they go. For example in the close up picture you have you can see LT-RR that one is the Left right rear bracket. This should help you figure out where they go