The decision is made on an application basis I believe, not each person in the application. So they would not accept you and refuse your son and husband. It would be altogether or none kind of deal.
Although, the refusal on medical grounds is made based on a 10 year calculation of financial burden the subject will put on the Canadian health/social system.
You can find more info on the technical details here: http://www.cic.gc.ca/english/resources/tools/medic/admiss/excessive.asp