There are two possibilities re. a litter of this sort. One is that the pups MAY have been conceived at different times. I know this can happen in other species. With the cat, the act of intercourse is needed to stimulate ovulation. I know this is not the case with the dog, but I think it's still a possibility in rare instances that some of the eggs may be relased a few days behind the others.
The second, and more likely possibility is that the mom has a malformation of the uterus, so that one horn of the uterus does not get as much nutrients or blood as the other, therefore the pups don't develop as well on that side. But that wouldn't explain the being hairless. They would just be undersized.
Reproduction in animals is full of surprises. The strangest story I've come across concerned a quarter horse mare I used to ride. She was sold to a horse dealer by her owner, because she had aborted her foal, and they couldn't get her to come into season again. At age 16, the owner assumed she was past the age where she could bear foals, so she got rid of her.
She was purchased on consignment by the stable where I was riding, as a possible school horse. She'd been out at pasture all winter, and was long-haired and unkempt. The stable owner got some good food into her, and with the help of the students riding her, she began to lose that long, scruffy winter coat. Well, the more hair she shed, the rounder she began to look, and pretty soon EVERYONE was saying, "Gee, if I didn't know she'd lost her foal, I'd swear she was still pregnant!"
Finally, the stable owner had the vet do a manual pregnancy check. "Yup," he said. "I'd guess she's about two months away from foaling."
He said he figured...in a one in a million chance...she'd been carrying twins. In 99% of cases, one of the twins will be reabsorbed, then abort, and take the healthy twin along with it. In this case, the other twin survived.
About two months later, she procuced a healthy male foal. The stable owner was over the moon, and couldn't stop smiling.
The horse's original owner was LIVID!!