You suggested they apply to visit CanadaNo, the issue here is that the parents wants only PR and no TRV.
"Since your parents are the applicants for the PGP2019, they should be able apply to visit Canada as super visa holders. As visitors of Canada, they could have being looked after by you and your siblings. Why you didn't apply for their super visa? Staying in Canada can be extended."
Which is why I said visiting isn't an option if he can't pass the medical.