From what I was able to read in 2.5 and I may be wrong but basically it had some uprising in heaven from the god of destruction and he almost disrupted the balance between soul beasts and humans then it had a fight to stop him, his wife which was the god of life sacrificed herself to stop him. im guessing that the two lights that were trying to come together was the gods of life and destruction trying to be together but because of their godly natures it kinda makes it impossible i could be wrong on some parts
I've done some research in DD2.5. Spoiler The second child Tang San and Xiu Wu is boy. His name's Tang Wu Lin. Our Tang Wulin is him? For exemple similar to Tang Wong in DD2. Maybe the Old Tang is Tang San's memory? Another tip is appear trident of the forehead Tang Wulin when he fight which evil soul master?