I let them live here to "get back on their feet" & they won't leave. I have to sell the house & they won't get out.

ANY question on law needs to include your general locale as laws vary by area.

You need to give them written notice to vacate and if the refuse, you need to go to court for an eviction order. The exact process will depend on your location.

It's in Illinois.

This site details the process:
Illinois Eviction (http://evictionresources.com/eviction_process_articles/illinois_eviction_process.html)

Unless there was an agreement to pay rent, then you have to give them the 30 day notice that you are terminating their tenancy. After that you go to court as indicated.