And then he can begin inquiring into their true names. It seems just crazy enough to be true and if it is true, does one lead them or are they more of a cohesive unit? Let's say they do have a leader and there is one Joker that reigns supreme.
Many comics have said that Sans is the older brother... But I haven't gotten any proof yet. It makes sense that Sans could be the older brother... But it makes just as much sense that Papyrus could be the older brother.
I've always felt Sans was the older of the two. Part of it is Sans's attitude, the fact that Sans pays for their house, that Sans reads Papyrus bedtime stories, and that Sans is constantly looking out for Papyrus. Plus Sans is way more powerful than Papyrus.