Well, if you need four bedrooms I suggest you book an entire house with four bedrooms it is a lot easier. But yes, if a host has several individual rooms available you can book as many as you want, but there is a catch... You have to make a reservation for each one individually. Find the property you want, send 4 individual requests and speak to the owner, tell them what you need and ask them to block the dates so that only your requests can book the rooms, they will probably give you to the end of the day to finalize all reservations. But beware, if you book more than one property (rooms in this case) for the same date you will not get a refund if you decide to cancel it.