Realistically, any horse should be able to direct rein as that is normally taught before they learn to neck rein. However, if it has been years since they were ridden with direct reining, then it may take a bit of re-introducing to remind them of what they are supposed to do.
Truthfully, though, if they already neck rein, I would just ride them that way.
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I agree on the snaffle suggestion, but one other thing that I feel should be mentioned is that since you don't know their tack history, they may not be used to being ridden in a snaffle.
If a horse has been ridden in a curb bit for a long time, then they may not be as responsive in a snaffle as they should. Of course, since you are new to these horses, you should really ride the first few times in a smaller, safely enclosed area like a roundpen or small arena. That way, if something happens, there is less risk to both you and the horse.