"The Prophecy" contains the history of the first Game (
Divine Divinity) and "Child of Chaos" the back story of
Beyond Divinity. There is no mentioning of the Sourcemagic in the novellas, since Source was introduced in
Divinity: Original Sin, but they explain what the Council of Seven and the Lord of Chaos is.
They are a fun read. Just don't be confused when you read, that they call "Rivellon" a country and not a world. It started out as the dukedom of Ferol in the first game, then it became the name of whole world^^.
@Lacrymas
I always thought the House at the End of Time existed in the far future, so that the cleansing of Source was something that happened many centuries later and was something for the "new world".
If my theory is correct, it would be logical that the Source is still tainted, since the Source Hunters still have to fight the last battle at the end of all time.