The 60-day requirement is if you have more than one lodger, so yes, the fact of another lodger would have to be disclosed.
I am not an expert, but I don't see that your sister and girlfriend have a tenant/landlord relationship with your mother, since there has been no rent paid, nor any contracts signed.
My recommendation is speak with a tenant/landlord rights organization for basic information. They'll usually give that pro bono.
Here's some online resources: