Only if it's late month already. In the beginning I don't think so. However some breeders told me that if the horse becomes very greedy in grain and don't like her sides to be brushed it can be one of the signs. Not sure how true it is though....
Keep track of when they should be coming into heat again. If they don't come back into heat (you should be able to tease them to the stallion to tell easily) then there's a good chance that they are pregnant.
Sorry, the only true way to find out is by a preg test. Many mares "come into heat" even if they are pregnant, and some will even accept a stallion all during pregnancy. (we own a couple who will do that, and they must be kept away from the stallion for safety reasons)
And the not liking to be brushed or touched is totally untrue. An old wives tale. Sorry.
I have to ask, why don't you want them vetted? If they are pregnant, you will need to keep good track of their weight. I like to make sure they have extra calories for that baby and also vitamin supplements. The health of your mares is extremely important.