I'm no lawyer just a simple dirt farmer, but I think you want a contract drawn up that says you are buying the farm, and you want some money to exchange hands - a down payment. The rest of the the terms can be whatever. You want this signed by whomever legally controls the property.
Since family is involved, you can get into trouble if you are getting a substantially good deal. The govt will think you are avoiding taxes. Disgruntled relatives will be able to use that... Certainly you can get a deal and not top dollar, but beware of trying to steal it....
A lawyer schooled in land could write you up a quick contract that is nice and legal, have the right people sign it, and keep things nice and legal looking. They will run a title search, and handle the paperwork, all for under $1000 typically, and typically split between buyer and seller.
Under your deal, I think that would be money -wisely- spent.