Well, my 2 cents is that both mares are indeed pregnant. It seems odd that BOTH mares would be acting this way at the same time. But, then again, I've never personally bred a mare so I don't know. Just my opinion.
I'm glad that you've found a vet that is going to come soon so you can know for sure! It'll definitely ease your mind.
If it turns out both mares aren't pregnant, as long as they are healthy and your able to properly care for the foals, I don't think there is any reason why would couldn't re-breed. Talk to the vet though.