A double side by side stroller would be challenging I think on the ship. The halls can be quite narrow. It would be hard to pass people in the halls with the double. I would look into a tandem if you want one stroller or two umbrellas (with connectors) if you want side by side. We have taken the umbrella before which did its job, but got a little bothersome over cobblestoned streets or long walks (just doesn’t handle rough terrain well & is shorter than a normal stroller lol). Also didn’t have the bottom basket for long days. What about a Sit & Stand? It’s tandem, and decently priced for travel. You can fold it up at night if you need the space.
Also, we have never really used the stroller on the ship itself. Just for time off the ship and walking around towns.
For reference, we have 3 young kiddos. We cruise often. Each kiddo started cruising around 5 months to a year.