Can my landlord allow the realtor to enter our home without our permission when we aren't home?

I'm one of four renters residing in a fully lived-in duplex. Landlord decided to tell us he was selling the house about three weeks ago. None of us are "o.k." with the realtor showing our place without the landlord or ourselves present. Landlord is stating that he can give keys to the realtors, they can put up a key box, and they are allowed to "show" our house with his permission as long as we get 24 hour notice and without landlord/tenants being present. Is this true?