You need SPC front camber adjustable ball joints to get a proper alignment, or you'll chew threw tires every ~5-10K miles. You can't have different tread depths... anything more than 1 or 2/32" of an inch between front and back = you need all new tires. The awd system will be fighting itself basically due to the difference in tread depth. I'd measure the tread depth of that other rear, and get it replaced asap. I'd also compare see how much is gone from the fronts. If it's 2/32" or more, you'll need 3 new tires. Sorry to be the bearer of bad news, but it beats buying a new transmisison. Get those SPC BJ's and a proper alignment ASAP!