
Just to add to the advice you will get, hopefully - don't cut the cord if you have to, tear it. Unless somebody has told you - newborn puppies can't regulate their own heat, so the area around the box needs to be kept at a good heat - around 80F if you can so when mum leaves for a comfort break, they don't get chilled.
For the future - NEVER leave an entire pair together. Once you see him taking interest in her, and know she's due to come into season, SEPARATE THEM. There was no point leaving her with him until day 7 ..... no two bitches are the same, some ready to mate earlier, some at the normal time, and others into the third week. And from the moment he was aware, he'd be ready and waiting. So what happened was pretty much inevitable and frankly you were darned lucky neither was injured in the tie, with nobody right there.
It's good that you sell the puppies for a basic fee - I'd set it at what people would pay a Shelter. I firmly believe all puppies should have a price, if only to show commitment on the part of the new owners - otherwise it's easy come, easy go. Without getting into whether anybody would buy them cheap to sell on as a 'rare mix' - shudder. If you can do the same check re the home that Shelters do, so much the better and if that means going to see the proposed new home, do. The breeder of my foundation bitch, experienced and in the breed for years, sold a puppy to a family who looked ideal. When they left with the puppy, she found they'd left something behind and ran to the gate to see them putting her puppy in the boot of the car WITH A LOAD OF OTHER PUPPIES. Had she not gone out there, goodness knows where that puppy might have ended up. Needless to say she took it back!