Typically if you sign a 12 month lease, you're agreeing to rent the place for 12 months. Without seeing the lease and reading it word for word, it's hard to say, but that is usually the case. It's also usually difficult to break out of without taking a huge hit money-wise. IMO, it sounds like they are being pretty reasonable by letting your brother out of it if they can find another tenant. You can ask, but maybe they can put it back up as available to help find someone too. It's a toss up, but essentially your brother would be renting a place he isn't living in. He can take the chance and continue to pay rent month by month, hoping that they find someone soon. Or he can just pay the lump some of the remainder of the lease and walk away. Chances are good that they won't just let him walk away without any sort of penalty.
My girlfriend went through the same thing recently. I wanted her to move in with me, but her apartment wouldn't let her out of the lease unless they could find someone to take it for her. She was only 2 months into a 12 month lease. She had to keep paying rent even if she didn't live there. The apartment complex put it up as available though, and luckily they found someone to take it so she only had to pay one additional month. In fact, they even prorated it since the guy moved in about three weeks into the month. I thought they were pretty reasonable given that she signed a lease for a full year.
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