Brandon said that Melanie's involvement in the cult was the reason why she wanted out of marriage (not unlike Lori's experience), so at least Melani seems to have been indoctrinated. Alex doesn't strike me as a religious person, so I'm not sure what was his motivation. The anonymous family member mentioned on GH that Alex and Lori discussed how they were going to spend Charles' money even before Charles' death, so he could have been in it for financial gain. Both Alex's and Melani's partners were allegedly part of the cult. I don't think Lori would hide seeing Chad from Alex and Melani, though maybe she made it look like friendship at first.