Looks like you guys had a great hunt! Nice bucks!
Besides getting the hide off as quickly as possible, if you can, hang it for 7-10 days just like beef. Even shoulders become tender.
As I have been too lazy to build the walk-in cooler, I have found these pricey coolers (like Yeti) can be put to good use. A bag of ice, a quarter, a layer of ice, another quarter, topped with ice; leave the drain cracked so water doesn't accumulate and tilt it a bit. Left in shade, checked every 3rd day or so and topped with ice. For working stiffs, the next weekend is used to cut and wrap. For those with more adjustable schedules, let it rest for at least 7 days, 10 is better. Just like beef, it makes a noticeable improvement in tenderness and taste. Antelope is one of my favorite hunts and game meats on the table.