There is much discussion of their sources, and the way they changed the tales after they collected them, especially from one edition to the next. There’s a very good article by Jack Zipes here http://publicdomainreview.org/2012/12/20/the-forgotten-tales-of-the-brothers-grimm/, and don’t forget the Stephen Sondheim musical, Into the Woods.
I can read them in the original German, which is a help, but I haven’t yet dealt with them systematically.
When I first started storytelling, in 2002, one of the first tales I told was The Tailor’s Three Sons, which I call The Able Table, the Double-Ended Donkey and the Stick in the Sack.
Here are some images associated with it:
I tell The Brave Little Tailor without reference to texts any more, and the same is true of The Devil’s Three Golden Hairs, which I now entitle The Lucky Boy [because that’s what it’s really about], and from a very early date I renamed The Bremen City Musicians as The Village Band and used the name of the next village along the road, which made the audience involvement all the livelier, especially at the climax, where all four animals join in at once:
So many tales appear in Grimm that also appear elsewhere, in different versions, that I have lost track of what I have taken from where and what I have changed to suit my own sensibility. I have told The Dancing Princesses quite recently, and given it a personal [but justifiable] slant – but some of the details come from the Andrew Lang version, and some may even come from Walter de la Mare. Certainly my male protagonist is not a soldier. I also observe that I have made the same change in this story that I made in The Six Swans, namely that the youngest daughter is the child of the king and the wicked stepmother, which has consequences…
Up to now, I have avoided the famous tales – no Cinderella, no Rapunzel – perhaps because I want to tell unusual ones, from lesser-known sources. No doubt the time will come when it feels right for me to make these other tales my own, or when I have time enough to make my own selection from the whole range.