JMO. . . .You want the game to move away then let them have access.

This land is owned by your family who likely worked hard to buy it. While you can be a nice guy, no body gets a free ride, if you really must give in let one of them buy a lease from you at a fair but high end of fair price and have a good set of rules defined, no guests, no drives, guns perhaps Bow only for your land etc.

Sounds like the only reason you have any game around is because these guys have not over run your land.