PNR doesn't matter at all for any guest. There are some rules around the guest needing to be on a delta flight (or skyteam/partner (this may vary a bit depending on exactly how you're accessing the club)), but in general they don't need to be on the same flight with you much less the same PNR.

I don't really understand the 2nd question, if they're accessing the club with their Amex then why would you need to use a guest pass for them?