If you are a legal inheritor of the property and are current with the taxes and other costs the property incurs, you should have at least a 50% say in how it used and receive 50% of any lease fees. If this was me, the first step would be to confront the uncle and let him know that since you're a 50% partner in this property that he has to work WITH you as far as leasing/renting any portion of the land. The next stop would be an attorney to find out just what this partnership means and involves and get some legal definitions that your uncle can understand. As for the leases, since you were not invited to be involved with their lease even though you have 50% of the say, I'd tell them "sorry', but this has to be moved to the front of the property since this portion of the property here is a hunting land...note the blind".

Do you get along with said uncle? If he's aware that you inherited your father's 50% of the property and are current in taxes and costs, why did he not involve you in this lease? Personally I's find out what the deal is with him by talking to him but I'd let him know that when that lease expires those guys are out unless they agree to relocate to the front of the property. I'd let him know straight forward that any leases or renting will require that you be involved and that 50% of any money trading hands is to go to your pocket. What insurance measures have this lease person taken out to protect against liability/damage?

I'd be some kind of miffed at this but would give the uncle a chance to explain things before I got into the legal community, but would make it perfectly clear that that's the next step and that you will not allow being walked on or circumvented. That's not right either.