I work in an academic research lab in the US. I have substantial reason to believe the PI of the lab does not actually have a PhD. There are currently two PhD candidates in the lab working under the PI. If it were revealed that the PI's PhD is a farse would there be negative consequences for the PhD candidates? What if it was revealed after the candidates completed their PhD?

No requirement for a PhD supervisor to have a PhD at most universities.

So, its not a problem!

yes, agreed, no requirement for phd supervisor to have a phd, so don't worry.

Are you suggesting that the PhD you PI claims to hold is not genuine? Like he bought it or something?