The bold part above leaps out at me. I think you might be right. Allowing their Scientologist kid to get into a relationship with a non-Scn is not something I think a "true believer" would do, for the precise reason that a non-Scn boyfriend/girlfriend might pull the kid away from Scn, and be a source of "unwelcome" news about the realities of Scientology, particularly in the Internet age.
It might be that the parents are (to some degree) "on the fence". It might be that the parents are financially dependent upon the first-generation true-believer grand-parents. It might be that this recruitment attempt may be an attempt at "hostage taking", to ensure the parents stay "in". I don't know, I'm throwing out guesses.
In the meanwhile, it's good that your kid is immunized. Keep your kid reading about the stories of others. Watching Leah's series would be good, if kid has not already done so.
Yes, these are some of the same guesses I have.