Can you use it as a double with one behind the other rather than next to each other?
Well, yes, you don't really use it as a double with only the seats in front. One of the configurations, the double one, is literally one seat behind the other, and it is also called Twinni (when sold only as a double, and you can do that with the triple, too, with the right adapter). Check the Twinni stroller to see what that looks like. And also, consult the manual, where everything should be explained.