If my opponent has a creature with Sigiled Sword of Valeron equipped, and I steal it with an Act of Treason effect, then attack them, who gets the attacking knight? Don't they still get the attack trigger because they still control the Sword? Can they put it into play attacking me on my combat or are they forced to put it into play attacking themselves. In a multiplayer game can they make the token attack some else?

I think you would get the knight, since it when it says "Create a token" it's a implicitly saying "[You] create a token."

No, you gain control of the creature but not any other permanent attached to it. Sigiled Sword is referring to its own controller in its ability, it does not grant the ability to the equipped creature.

The controller of the Sigiled Sword creates a token and because they're not the active player, the token enters the battlefield not attacking.