I'm Doug, and I'm very sorry to hear of your situation. My goal is to provide you with excellent service today. I am a licensed GA attorney.
Unfortunately, when property is owned by more than one person, each owner having an undivided interest in the property, each owner may use the property as they please---even if it is disturbing to the other co-owners.
While it only takes one owner to legally invite a guest onto the property, it takes the consent of all owners to deny someone entrance onto the property. For that reason there is nothing that you can do to prevent your siblings from inviting the outsiders onto the property. While this is indeed a significant potential liability to you, that fat will not allow the court to prevent these invited guests of your siblings from coming onto your co-owned property. There is a solution for you though. Let me explain.
What right you do have however is the right of Partition. You can apply to the GA Superior Court with a petition for Partition of the property. If the property is capable of being subdivided into 3 parcels with each parcel being of equal value (not usually doable if there is only one residence on the property) then the court can order that the property be divided with each of you taking an equal share. Alternatively, if that is not practical, the court will issue an order that the property be sold and the proceeds divided between the three of you (or one or two of you could buy the other(s) out and keep the property without the need for a sale to a third party.
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I wish you and yours the best in 2015,