What class are you migrating to Canada under?
You can sponsor parents under the PGP program if you are a PR, but you need to have 3 years of Canadian income and meet LICO. Either you or your sister can apply (not both). PGP is done as a lottery with limits on the number of applicants chosen each year (10,000 for 2017 with significantly more applicants that available spots) and you need to meet LICO during the entire process. Realistically, if you are just landing as a PR, with no Canadian income from any source as of yet (including your spouses), you meet LICO ($45,712 plus 30% for a family of 4 in 2017), it would be a minimum of 4 years before you could qualify to submit an application. Then you have to be picked in the lottery, which really is luck of the draw.
If they include your brother in the application as a dependant (he would need to meet the age limit or be dependant) and he is found medically inadmissible, all three would have their applications rejected. Your in for a long, potentially difficult task.