Hmmm. A few thoughts ...
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You're trying to get DS2 used to sleeping in a bed, and used to sharing a room with DS1, and used to sleeping in a different room than before, all at the same time. I'd try to do these one at a time - maybe starting with cot in DS1's room, with DS1 maybe sleeping somewhere else, then cot in DS1's room with DS1 there, then bed in there.
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A white noise machine (or white noise CD) helps cover random noises.
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Can you sell sharing a room as a priviledge to DS1, to get him to help?
My two are three years apart, and have shared a room when on holiday. We put them down separately, and tell DS1 sternly that sharing a room with his brother is a treat, and we'll stop it if he makes noise etc etc ...