If the young people haven't yet got a job for when their student status ends (imminently), I did read that one way to swerve paying CT is to sign on for Jobseeker's Allowance immediately. For as long as someone is claiming it, they would be exempt. Obviously it's not ideal but if it may take them a month or so to find a job, it would save them a bit of money.
And it's also assuming that all 'eligible' flatmates will agree to split the CT bill due. If say four should pay but only two or three agree to do so, it means the others still have to cover the full amount which is unfair.