accommodations for one night / two nights

I'd say

dude's suggestion is good in AE, AFAIK. If you're writing/speaking in BE, on the other hand, accommodation is regarded as an uncountable noun and therefore sounds odd with an "s" on the end. So, in BE, you could use "accommodation for one night / two nights" or your first two suggestions: "one night's accommodation" / "two nights' accommodation". (Your other two suggestions are not correct.)