I was able to lockpick all of them, but by then beast had max thievery and possibly a bonus or two from gear. I don't know the lockpick requirement, but I never found any magical mechanism other than lockpicking.
There wasn't really anything special in the magic chests.
But that scroll is a great idea! I'll have to try that out on my next playthrough. I remember using it on a random barrel of fish and nothing happened.
