Hansel and Gretel

After reading all the different versions of Hansel and Gretel I have to wonder where exactly did the Grimms Brothers hear their version of the tale and how did they story before they made changes to it. I mean, come on, very few of the versions have even a handful of the the same elements. Three of the stories are the same, they only reverse the role of the girl and boy, two of the story's are about siblings that are of the same sex who rescue anywhere from 3 to 7 siblings.
What I've found most interesting about the tales though is that the stepmother is always portrayed as the evil one (putting aside the tales with ogre and witch). I can't understand how a father who simply goes along with the plot to abandon his own children, thus dooming them to death, could be considered a nearly faultless father. How hard would it have been to simply man up and say no?