No, in general the system is not set up to allow sibling immigration under family class. Only spouses, parents and dependent children.
So really your only option is to apply for your parents PR (when the program re-opens on January 4, and if you qualify with your spouse for income requirement), and include your sister as a dependent under their application. Any siblings aged 19 or over are not dependents so would not be included in the application. So assuming your eldest sibling is over 19 and can be left off the application, their medical condition may not have any effect on parents/youngest siblings app.
In theory once parent's app is approved along with youngest sister, they can all come to Canada to land as PRs, but then parents are free to return back to home country if they want to. If they eventually lose their PR status due to not meeting residency obligation, it would have no effect on youngest sister's PR status as long as she was staying in Canada.
Just note the parents sponsorship process is very tough to have your app accepted since they only accept 5000 per year and should be received on Jan 4, and the process can be quite long (expect at least 4-5 years).