A4 Rear End problem - One tire worn bald

[MBDA4]

ORIGINAL POSTING TITLE WAS "A4 Rear Axel problem - One Tire Worn Bald" -- with this as the description of problem:
"My son’s A4 Avant has worn the right rear tire completely bald in less than 3 months!
No online searches have yielded results so coming here to ask for help determining the cause..."

Since then I went to son's place and discovered that the problem is much different than when I posted. Would delete this thread and start over if I could.
BOTH rear tires are worn bald while the fronts still have most of their tread. All the same tire make, model & age - these are his Spring/Summer wheels & tires... installed them in April. The tires should have had another 20K miles or more.
In 3 months time (approx 10-13K miles) the rear tires are bald, with the right rear worn to the steel ply on the inside. It's obvious that the rear is very out of alignment, but, am worried that front diff may be slipping or not engaged at all.
Could the problem simply be need for aligmnment?
Have reinstalled Winter tire set & will get to a dirt road to test if all 4 wheels are pulling...

Tires are Bridgestone "Turanza Quiet Track" with exception of the left front being a Bridgestone "Serenty" = modern replacement for the Turanza.
As you can see from the photos my boy never checks his tires - just drives

LEFT REAR/RIGHT REAR




LEFT REAR/LEFT FRONT




RIGHT FRONT/RIGHT REAR

[Larhal]

My son’s A4 Avant has worn the right rear tire completely bald in less than 3 months!
No online searches have yielded results so coming here to ask for help determining the cause. Help!

A Picture could help .

[MBDA4]

Appreciate your willingness to weigh-in on this. Will get a pic posted soon…
In the meantime will elaborate. Tire is worn bald completely and evenly, so it looks like a slick tire now - while the other rear tire still has a decent amount of tread.
All internet searches came back with others’ alignment problems and “uneven wear” on either inside or outside edge. That is not our scenario - so I doubt it’s alignment.
Realized this a.m. that it could be something as simple as the boy driving for a few 100 miles on an under inflated tire. It’d be easy for him to overlook right rear being low. I didn’t stop long enough during my visit to check air pressure. Will do that when I get pics…

[EuroxS4]

This all depends. Were both rear tires changed at the same time?? Are both rear tires the same make band and model?? Is the right rear caliper dragging or hanging up at all??