Women and kerbs eh

My missus smashed into a kerb on Friday night, kerbed the wheel badly, tyre was a write off but she still managed to get it home. Come through the door crying about the wheel and the tyre. Wheel was changed with a new tyre first thing Saturday morning. Saturday afternoon, she done the EXACT same thing to the opposite wheel and tyre, big chunk out the wheel and the tyre and an instant flat.
I was actually speechless at the stupidity, I never said a word to her or I no doubt would have been murdered
Anyway, looking at that sidewall in your pic, yep, that tyre needs changing. The RS6 is a big heavy car and those tyres come under a lot of stress. As to whether you need to change the other one with 5mm remaining, Hmm. In theory and for what's best, I'm sure you know the answer. In practical and reality, tough one to justify. Measure the other two tyres to see if there's a better match available, one may be at 7, the other at 6. Pair the new 8 and 7 together and the 5 and 6 together. It would be very minimal difference.