We've had our son and daughter in-law sleep on the dinette. I like to say, it'll sleep one comfortably, and two uncomfortably. We actually bought the yacht bedding mattress for the dinette as the cushions aren't particularly comfortable. My son and his wife slept ok for the night on it. They're young. We know when we're having them over, so most of the time the dinette cushion and mattress is kept at home in the garage. I've also had my mom onboard and she slept on the dinette mattress. She's short, so getting up and down on the bed was a bit more challenging. I brought a step-stool to help.
When we're on the boat, where do we put the cushion (or mattress and cushion in our case)? We throw them in the v-berth until the evening.
Some folks use sleeping bags onboard. We don't. We use sheets and such for both the v-berth and dinette. None of the beds qualify as a "twin" or "double", as they're odd shapes. It's a 27' boat.
I would say, the boat is really built for 3 adults. 2 is preferred, but 3 adults is fine. Our daughter sleeps in the cave comfortably. She's also short (4'10") which probably helps. Two in the v-berth and one in the cave. On occasion, it'll sleep up to 5 adults.
We spent last boating season on our RT27-OB, 3 adults, 3 dogs, and went from Everett, WA to Glacier Bay, Alaska. 2,600 miles over 55 days. 180 hours we put on the engine. The boat was plenty comfortable for all of us onboard.