I have somebody making a plugin for that for me. He's also making a plugin so that TNT affects entities but not blocks.
And as for when there's two left, how do they know they didn't already kill the murderer? It doesn't matter if the murderer's alive or dead, the guest who manages to get 2/3 of the clues together wins.
If you want I could simplify it and it could be all out war but in a mansion.