Unless the verandah between them is not structural, normally you can open the wall even when rooms are not connected. You would need to look at a map of the ship to see exactly where your rooms are. Most are able to open but some cannot. In the picture below, the green indicates walls that will open. The red indicates places where they do not open as they are structural.
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When we sailed earlier this year, the verandah wall between ourselves and our neighbours (that did not have a connecting room) blew open in the night so I know for sure those open.