#2-4 have too many "us"s They want us to turn on each other. -> They want us to start fighting They want to turn us against each other. -> They want us to start fighting and they are going to actively do something to get us to start fighting. They want to put us against each other. -> They are going to make us start fighting They want to get us against each other. -> They want us to start fighting and they're going to keep doing something until we start fighting each other. (Like #2, but more intense).

The first two have the same meaning. The third sentence sounds strange to me, I would say pitch instead of put (then it would mean the same as the first two. "They want us to pitch us against each other" The fourth sentence is incorrect. * Update - I Angela is correct, I don't know how I missed the second us :/ Voting her answer up