Puppies have weird issue with tails

I was hoping someone could help me figure out what this is. It's been on 2 of this dog's 7 puppies since they were born about 1 month ago. She was a stray but I've taken her in to look after her for a while. It hasn't really gotten any better and I want to know if there's anything I could do. The areas affected are the tail and for one of the 2, the paws have the same thing. The area appears lumpy and dark compared to the rest of the dog's skin.