Complex sentence: Some forty people of various nations and ages, who were on these islands, have to do a two-year-long journey on the comet, forming a mini-society and coping with the hostile environment of the comet (mostly the cold).
Split into simpler sentences: Some forty people of various nations and ages are condemned to a two-year-long journey on the comet. They form a mini-society and coping with the hostile environment of the comet (mostly the cold).