I have very recently dealt with the R & R of these rear trailing arms and the wheel bearing & axle shafts, etc.

It's not an easy job to replace the wheel bearings, but right now, you don't know if that's the problem.

Since you have already found some trouble inside the axle shaft boots, you might consider removing the axle shafts. The axle shafts can be foreshortened just enough to barely be able to get them out without having to remove the rear trailing arms, springs or shocks. This makes it a reasonably easy job.

You DO have to open the differential by taking the back cover off so that you can pull the circlips that hold the axle shaft in the differential.

To swap an axle on one side took me two hours total. Both sides should be less than 3 hours to remove and re-install.

Once you have the axle shafts out, you WILL be able to separate the variables regarding the noise(s) and find out who's the problem.

You will also be able to clean out the crud in the axle shaft joints and re-lube them.

You will also see if you've got a problem inside the differential. If those gears don't look perfect, you've got a problem there.

You will be able to turn the wheels without the diff connected. If you've got a significantly bad wheel bearing, you should be able to tell.

This will help you to bound the scope of what you're dealing with. You may still have a problem in the axle shaft(s), but that isn't the grinding noise, the noise they make is a very low frequency kind of rumble, but you'll have to get that thing quieted down before you'll be able to evaluate that.

R & R of the axle shafts isn't that big a job. R & R of the trailing arm is harder; you have to deal with the springs. Replacing the wheel bearing assy is another significant task.

If you decide to take my suggestion on removing the axles for the evaluation, I would suggest loosening the boot clamp on the can at the outer joint and pushing the boot off the can on that side. The reason is that to get the axle shaft out of the back of the hub requires the joint to be cocked at a maximal angle to the shaft. This kind of bending on an old boot can cause a leak. If you scoot it off the can, it won't get bent like this.

You will have to remove the diff mount and lift the diff way up to get the axle out, then lower it back down to take the cover off, pull the circlips and get the axles slid out sideways , but that's pretty much the extent of it; you don't even need to remove the calipers, although your parking brake problem will require some attention. You'll need new circlips; outer seals to the diff & Dirko sealant that's ~$40, but you'll then know if you got big problems (the diff), medium problems (the wheel bearing(s)) or some other minor problem.

Just a suggestion.