Of the options, choice D is the best summary sentence for the passage:
Father and Mother created a space for the family to stay during their long journey.
The passage describes Father and Mother disappearing below deck to create living space for the family and their belongings for the weeks of travel ahead on the ship. Options A, B, and C provide additional details or interpretations not conveyed in the original passage. So choice D succinctly summarizes the key event and circumstances described.