Without all the facts these complaints are not very valid.
First off, there is no way a cruise line allowed 4 in a cabin that could not sleep 4 people.
It is a fact of life that cruise ship cabins are SMALL, unless you have a big suite or penthouse. The sizes of all cabins are available. Did you not get the size of the cabin before you booked?
As Dizy asked, who did you deal with? Hal, a TA or internet booking.