Sorry didn't say Ventura.
I can't speak specifically for Ventura, but a twin or 2 berth is identical in size to 4 berth throughout the cruise industry. The additional beds drop from the ceiling, or on older ships fold upwards & flat against the wall. What your seeing on your photo is what you get in terms of space & size.
If you have a Balcony cabin then these do not usually have upper berths. The 3rd/4th Berth is a Sofa Bed.