From Divinity Engine Wiki
- call AddToParty((INTEGER)_Source, (INTEGER)_Target)
Adds the characters controlled by the user with User ID _Source to the party to which the user with User ID _Target belongs.
- A party is a group of all player-controlled characters from one or more users, along with these characters' totems (and in Game Master mode, also characters possessed by the game master). By default, all users are in the same party. Players can split parties by right-clicking on a character controlled by another user and selecting "Kick from party". From script, you can create multiple parties using some of the APIs mentioned below.
- All characters from a single user are always in the same party.
- Never add NPCs to a party, as many code paths do not support that situation (it is not possible with this API, but it is possible with another one).