“The Maharal explains that they only kept ????? ??? and not ????? ?? ????. But that was about Yaakov. I don’t recall, as of now, a reference to the Shvatim keeping the Mitzvos.”
The Maharal discusses the Shevatim as well. http://hebrewbooks.org/pdfpager.aspx?req=14210&st=&pgnum=234