Shared apartment. Landlord keeps on bothering

It’s a four rooms apartment. Very nice and expensive. Three rooms are taken. The forth one will be, according to the landlord said but for now it is empty since some months. Landlord keeps on coming inside the house just by sending a message in a chat some hours before he needs to come. Once is to pick up a delivery for a new forniture, once to clean upstairs. Once he sent a friend to sleep there, once he had to put some decorations on the rooftop. Is this legal? What would you do? Is it possible to behave like this or since he doesent have the residence here he should give us proper notice? He said he can do it since it’s a shared apartment. Is it true?