They would need to file a change of status petition with the USCIS and pay the appropriate filing fee as well as submit documentation proving that they have a qualifying family relationship to you, the principal H-1B holder, as well as proof of your status. As far as the timing of it, it can be done at any point up to the expiration date of the current L-1/L-2 EAD, as long as your wife is still in current L-1 status.
Answered on Mar 26th, 2012 at 5:15 PM