Your doe population probably is not the problem as there are definately more than just those two. The challenge calls i don't see working unless the one mature buck you have seen is in the area. The younger bucks have had their butts wooped enough to know better than to run into a fight. I would say just do your time in the stand and get a little luck on your side. The bleat may be the ticket if one of those bucks is within ear shot of you but as far as drawing them in i have never had it work for that.