For the last one, you could even have the effect be that one of the computer players declares victory (using the "declare victory" effect). Then you don't have everything dying when you lose, you just lose.
With the second one, Nixck's idea is good.
For the first, you cannot extend the wonder timer, but using some elaborate triggering, you could probably create a timer system instead and use a different building or something like that. AFAIK, the actual timer attached to the wonder cannot be changed.
EDIT: Just to clarify, the "declare victory" effect can only make player 1 win or lose. If player 1 declares victory, he wins. If anyone else does, player 1 loses. If you want any computer players to lose with the game ending, use Nixck's idea.
[This message has been edited by Sarn (edited 05-09-2011 @ 00:14 AM).]