Part bollox, part truth.
Unless there is an extremely restrictive set of site rules relating to property occupation (which I seriously doubt!), then friends and family can use your property whenever you wish them to. It's not a business although if the Maliye turned up and started asking questions, it'd be better for friends to have a written permission (from you) to stay in the property.
Technically, all tourist and temporary visitors are required to register with the tourist Polis - hotel records are open to inspection at any time by the Polis for this purpose. However, given the number of private properties, and private rentals, this requirement for independent visitors has fallen by the way side. You'd probably get an odd reaction if you popped down Fethiye harbour and tried to do it these days.
Let your friends and family enjoy your property and tell the EPK know-it-alls to bugger off.
JF