I’ve been thinking of a way to pit members of a party against each other without requiring them to duel to the death (usually bad for party harmony that death thing). It’s actually pretty easy. They are likely all members of their appropriate guilds - Soldiers Guild, Mages’ Guild, Thieves’ Guild, or whatever. All you have to do is find something they all want. Not something really important, something worth bragging rights. The queen lost her crown on a hunting trip. A thief stole the battalion’s colors. A rat ate the princess’ ring and ran off into the market. Something like that.
Well, the party really doesn’t care about all these bragging rights, but their guilds do. Instead of partnering up with their buddies, their party members, they join up with their guild mates to return the crown or colors or ring. More than likely they are running through the city, so even if they wanted to go around killing each other, it will really be frowned on. The whole point is to get them to use their non-killing skills to be the first to accomplish the task or retrieve the object. It’s all about the competition. Who will win? Who will come out on top? Which guild will prove itself the best, or at least the coolest?
They’re tough to run. You need to keep your players away from each other so one team’s clue doesn’t tip off the others, but you’re up to that. You have to make it difficult for each kind of team - combat, magic and stealth. But when it’s all over, they’re going to love you for it!