Basics:
4 guys live together in house renting from one of the guys parents. I re-signed a lease (for a second year) as a group requiring us to come up with $2400/month. I only re-signed the lease several months ago because I could not afford the expense of moving. Six weeks ago, i gave written notice to my fellow lessee's that I was moving out. In that time, all three have made no attempt to find a replacement roommate yet they have informed me that they would like to meet any potential prospect I find. I have turned down several people that were not compatible with the three. I could have easily filled it already. Isn't it the responsibility of all lessee's to find a replacement and not just the person moving out? Because the landlord's son lives with me he is coming after me directly - even though the lease is signed as a group. At this time, does he have the right to single me out or are the other three roommates responsible for paying my share since we signed the lease as a group?

Do I have a case to stand on based on their negligence of finding a replacement roommate? even when I gave six weeks notice and have proof of actively searching for a roommate?