You must be joking!!! There is no way I would put all of us in the same vehicle for even one full day of traveling. My brother runs a yota and my dad is buying an unlimited 4 door.
Whew! that changes the scenario completely. I was thinking the same thing reading through this thread: 3 men, 3 weeks, remote location, in a TJ?
So now you are solo in your TJ, and the other two rigs will have excess capacity to hold some of your stuff if its needed.
You never mentioned a budget, but i will assume its a factor. Here are my suggestions:
1. Everyone should get their HAM license and a 2 meter radio.
2. Your dad should get a Rubicon version, maybe add some off road lights, and then he's pretty much ready to go (in the new JK).
3. You might want to stick with 33" tires, but that depends on your twice a week wheeling that you are doing. The BFG KM2 is an excellent tire, as is the AT, or the new Goodyear MTR. I think the MTR is a better compromise between the AT and KM2, and might be more resistant to cactus damage with the kevlar sidewalls.
4. Adding a rear locker is an amazing capability extender, but if money is tight, a decent winch and winch bumper is better bang for your buck, and will help the other two rigs also.
5. front sway bar disconnects are cheap and effective. The Currie Anti-rock system is a little less cheap, but very good.
6. At least one of the three rigs should have a large electric fridge. The new ARB is excellent and holds 50qt, which is a lot. Maybe have two, one for food, one for drinks. With three weeks to consider, and infrequent ice availability, you will appreciate the electric fridge.
7. All three of you should have a full size spare. if the three of you ran the same size tire that would be best scenario.
8. All three of you should have an excellent tire repair kit. The Ultimate Puncture Repair kit is the bomb!
http://www.adventuretrailers.com/tirerepair.html, or the ARB speedy seal kit is also very good, but a bit less complete. Good for plugging tires though.
9. recovery gear, perhaps some sand ladders,
10. extra tent stakes (it can get windy!)
11. an Awning or a Kelty style shelter from the sun is going to be popular too