Under Who you can sponsor Option 2 it says If the relative you want to sponsor has a spouse, partner, or dependent children who will come with them to Canada you must include them on the same sponsorship application.
http://www.cic.gc.ca/english/immigrate/sponsor/relatives-apply-who.asp
My sister has a spouse and I am living alone, my parents are still alive bu they are coming to Canada, can I still sponsor my sponsor and her spouse?
http://www.cic.gc.ca/english/immigrate/sponsor/relatives-apply-who.asp
My sister has a spouse and I am living alone, my parents are still alive bu they are coming to Canada, can I still sponsor my sponsor and her spouse?