Larian Studios Forums Divinity: Original Sin 2 - The Modding Dungeon Divinity - Original Sin 2 - Modding Guides Tutorial - Companions/Party management via dialog.

If Scott allows me to add my findings :

For me it only worked with:

CharacterAddToPlayerCharacter(_npc,_Player);

With this _npc will follow the _Player and his portrait will be assigned and place on the right site of your _Player portrait.