For invitation and applying your parents for visitor visa, you don't have to be working. If the visa officer thinks your and parents' finances and other information outlined in the checklist are acceptable, the visa would be approved.
For PR, you/spouse only need to meet the LICO regardless you/spouse work or have other Canadian source of income. It doesn't matter if the applicant (your parents or in-laws) work or not. I just found out Leon has already answered this question earlier:
http://www.canadavisa.com/canada-immigration-discussion-board/sponsoring-parents-from-india-t76109.0.html;msg869199#msg869199
Immigration Forum
