Sounds like a time share. You would own a percentage of the apartment with a bunch of other people, You would have to book the time you wanted to use the apartment and you would be limited to the number of weeks you could book as the other people would be there when your not. Also lots and lots of rules!
usually not, you have to be the person who stays there, you can’t sublet. And you still have to pay your percentage weather you use your time or not.