I think 75 yards is plenty of room. Out of courtsey you may want to leave a note attached to his tree to inform him your set up next to him so he dosn't go postal if he happens across your stand. I'm would wager a bet since your family owns the land it won't be an issue. Also if he only hunts a few days as it sounds you'll likely not have much contact unless you hear each other shoot. Then it would be polite to help drag.

If you went through the trouble to find out who owns the stand why not contact him?