All instances of "if" here have the meaning of "since"; Job is speaking as if all these things were true. "Since the only home ... and since I have spread ... and since I have said" (See: [[rc://en/ta/man/translate/figs-hypo]])
Here Job speaks of being prepared to die as having laid his bed in the darkness. Alternate translation: "have prepared myself to go and sleep among the dead" (See: [[rc://en/ta/man/translate/figs-metaphor]])
These two lines are a variation to each other and are used together to emphasize how desperate Job is. (See: [[rc://en/ta/man/translate/figs-parallelism]])