It's difficult to judge if that might be correct or not (or how to adjust it) without knowing the weights. For instance, depending on the baling process, half a bale might either equal 15 pounds or 50 pounds.
Yes your horses are skinny. Instead of buying a horse trailer, buy quality hay, feed and a scale. Also some dewormer as I see worm bellys. Also have a vet check teeth and fecal counts as well as maybe some blood work to see what they are lacking in their diet.