'Aven't a clue, mate. Sorry. Mostly, I make this stuff up, and then frantically e-mail Anu and Avy and Manoj begging them not to expose me for the fraud I am!
Actually, this folkloric stuff was gleaned by me on Gran'ma's knee and so on, so there are really no written references. Try a google search - "the Nairs of Kerala" (it seemed to throw up some interesting looking bits and pieces). Also, I heard years ago that the Nairs' matrilineal system was pretty much standard reference for sociologists using the SSSM model who needed grist for the
tabula rasa mill.
Try
http://www.gotop10.com/KJ/khnairs.html. Seems the best of the google lot - quite detailed. The conclusions drawn, particularly with regard to origins, seem to me to be too speculative to warrant the conviction with which they are presented, but the details of customs seem about right.
cheer
the sunshine warrior
ps. post-Post edit: Also see an interesting page from a discussion forum,
http://forumhub.com/tnhistory/2315.24415.07.41.54.html, that nevertheless appears to be one whose primary topic is Tamil. Strange are the ways of South Indians eh?