@Sian48
You need to create a listing for each appartment, as each listing will have his own booking calender. which is mandatory if you want guests let them book seperately. You can use the duplicate funktion to create the new listings form the existing one, which could save some work. Also when you have multiple listings, you can use the "professional tools", like the multicalender. It gives you the opportunity to make certain changes on all listings in one operation.
Best regards,
Emiel