*ahem* I'm not an athiest/agnostic. But my advice still stands. Your whole attack is still too blatant. I know of what I speak. I'm a regular Christian who married a Jehovah's Witness. In the first couple years of our relationship, I was sure the Holy Spirit could overcome the JW indoctrination in short order. I no longer believe so.
If you are bent on salvaging not only your relationship but converting your study partners, you better shut up and read Steve Hassan's "Combatting Cult Mind Control" first. Otherwise you may make some newbie mistakes that might permanently turn your gilrfriend and friends against you.