If Jews live in a chatzer with a gentile and the Jewish houses are connected via windows and they make an eruv via the windows they can't carry via the courtyard.

If 2+ Jews are travelling on a ship (e.g. a cruise ship) and have separate rooms but eat together they are a single entity. If they also eat separately they are separate entities vis-a-vis eruv chatzerot. They have to acquire the rights from all the people on the boat unless they execute the transaction before the owner rents the cabins to individuals.