As someone who completed the game and sometimes checked it to see weather i'm missing some stuff or not i can tell you, that the gamepressure walkthrough is only lacking a few options with quests. Otherwise it's probably the best walkthrough there is.
Spoiler regarding "thorn in the side":
As for the quest "thorn in the side", that quest itself is missing "the good way" to complete it. Once you have accepted the quest you can still save the prisoner, but you will not get a quest completed message. I also found it hard to kill that man with the evidence that pointed to him being wronged. I took a load, told the questgiver to go f himself, mindread the guard and rigged the prison teleporter so it took the captive to his home village. Changing the destination is easy, you do it from the control panel of the teleporter. Just set the destination to high hall and you are set. You fail the quest, but it's not that big deal.

Spoiler on williams:
Williams is trapped in the mine in broken valley. The map is a completely separate map from main orabas Fjords map. The entrance is near the teleporter you used to get in Orabas Fjords in the beginning of chapter. See the main map here:
http://guides.gamepressure.com/divinityiiegodraconis/guide.asp?ID=8265
Broken valley entrance is marker 5.1

Spoiler on Laura:
You can find her on a high cliff you can reach as a dragon. The place is near where you started the orabas fjords map. Again, look at the gamepressure map if you can't find her.