There is a difference IMHO between "soul groups" and "soul mates" in the most conventional "definitions" of such.
Soul groups are allegedly souls that you travel with repeatedly within and without incarnations, in different roles to both help the spiritual growth of the soul, both as students and teachers. Often times, the roles and lessons, in a broad sense are agreed upon before the individual incarnation.
Soul Mates on the other hand...well this is easier...
Soul Mates and Twin Flames
I haven't read the Michael teachings in entirety yet, however it seems that they are using the term to describe something else...JMHO of course.
Many channelers claiming varied teachings/hypothesis. I'm sure there may be some truth within them all, and then again perhaps not ....there's Cayce, Jane Roberts, Esther Hicks, Neale Donald Walsh, Madame Blavatsky etc.....along with Yarbro.
Guess the question may be, why are they all getting different information?