Ive found the second key in barnabas cave. You take the dragon form up to the highest teleporter in the cave next to the dragon skeleton, then after teleporting, follow the path down until you get to the second last room. Inside this room is a few crypts. One of them is broken open, inside is the second key. I hope this helps.
I discover an area I didn't go/find earlier and when I see our pictures and go in the game, I found the area and chests you mentioned! I'm sure I didn't go there because I must kill Black Ring Memebers
Me too (on Xbox) can't open that chests with Lock Pick! And can't find a key for them!
On 7th of february 2015 : I start a new adventure in the Divinity world of Original Sin, it's a Fantastic Freaking Fabulous Funny ... it's my All Time Favorite One !