My default Victory Condition idea is the method I call "Impredictable Diplomatic":
It is based on the idea the same Team buddies cannot fight each other but can willingly miss open collaboration, or even secretly make some little naughty deal with enemies, leading to possible odd events like the example:
-One day Ultramages and Paladins agree to join forces to destroy their common enemy neighbour the Witches, and agree they can abandon Testosteronics by letting them lonely fighting any aggression from Amazons and Matrons... -
After all, the fact Team Buddies are just 3 and not 2, just allows many opportunities of impredictable diplomatic events! :D

The technical points allowing "Impredictable Diplomatic" Victory conditions would be:
1) The game ends when the last SC of the last Country of a Team is conquered, of course by anyone of the enemy Team
2) The winning Team can be at that point still of three Buddies, but also of only Two survived or even of one only; the single Victory that makes a player the only winner would be the number of SCs: the buddy owning the most, is the final winner of the game

Another idea about Victory Conditions is the one of Oli (I will call "Straight Military") :
When a Country is conquered its last SC and then defeated, the game ends immediately and the victory is for the opposing Team

My question is: but all the 3 players to be winners at same time is technically possible?

I think this method would make all Team buddies very protective each others, just to avoid the common defeat, and encourage straight collaboration with little or no intrigues... But what would happen if a player leaves games and the Country into Civil Disorder? The Buddies would be in great difficulty about trying to defend a non playing country from neighbours quicker attack... :|

It's technically not possible to have more than 1 winner. We can make a draw with many players, but the software can't handle 2 or more players winning the same game.

The draw can be programmed to be automatic, or always have to be agreed by every player?

The draw can be automatic. But it does distribute the points even between all remaining players, so the other team need to be destroyed completely (for real or automated) and all remaining players get the same share of the pot.

Good, then it can work that way!
But about the classical problem of a player leaving its country into CD? He would condemn own Team buddies to nearly sure defeat...