Are "devre mülk" (timeshare ownership) and "devre tatil" (timeshare holiday right) the same thing?

No, they are different. However, if your timeshare ownership grants overnight stays in a property across multiple periods, the rules on timeshare holiday contracts may apply. Also, timeshare ownership (devre mülk) is a real right registered at the land registry and enforceable against everyone. Whatever it's called — devre mülk or devre tatil — we recommend speaking to a lawyer before taking any steps in this area.