Buy a season pass. It usually breaks down to if you ride 5 or more days you'll come out ahead in the end.
If you were just trying to ride cheap, your best bet would've been to pick up Loveland 4 packs, but you missed the boat on that one.
The best deal going right now might be the Shell buy one get one free lift tickets. Have your brother start buying his gas at Shell and racking up those vouchers. $20 or more in gas and you get a buy one get one voucher that's good at Copper, Loveland, Winter Park, and Monarch to list the mountains that would be a reasonable day trip from Castle Rock.
The other thing to consider is that you're gonna be coming out here during very high traffic times. Lots of holiday tourists will be mobbing Vail and Breck and lots of Front Rangers will be making day trips up since they'll be off work. Don't expect light traffic or short lift lines. I would fucking hate to make that day trip from Castle Rock that many days straight during peak holiday season. That's not gonna be fun. Fair warning.