Would add that if your parents have each other to depend on they aren’t also considered alone in their home country on top of your sister also being in the home country. Even if you are a single parent you aren’t guaranteed approval.
Unfortunately parent sponsorship isn’t guaranteed. I wish this was stressed before immigration because many seem to think that it is guaranteed when they move to Canada. I’ve attached an example of a single parent who was denied H&C. There are many people in your exact same position and many who have applied even longer than you have. Canada has large number of people immigrating but also an ageing population so it will never be possible for everyone to sponsor their parents. Would add that the general population now realizes how health resources are insufficient to deal with the current population that may also be a consideration going forward.
https://decisions.fct-cf.gc.ca/fc-cf/decisions/en/item/421303/index.do