Lynn,
You need to someway, if possibe, seclude them from the other dogs, and spend time with them. See how they act.
*If they cower-they may have been abused or a little timid-which can be helped sometimes and they usually make devoted pets.
*If they act normal-great.
*If they act hyper-in with the other animals or away from the other animals, I would pass.
*Since they are from a rescue, ask questions about the dogs you are interesed in and their personalities, they have no reason to lie, only to place the dogs with the right people.

I hope this helps, and maybe someone else will come up with something different that will help also.

June