Nothing in the world beats the feeling of having pulled 4x8 sheets of drywall straight up via the small opening next to the stairs, causing the sheets to more-or-less bypass the stairs entirely. Sure, your arms may shake and you may feel like you can't quite do it, but once it's done it is a feeling of outright dominance, human vs. very heavy object. I wondered why the stairs were built like that. I still don't know why, but am very glad, because taking them up the stairs the traditional way would have been far far more difficult.
Two people are definitely a must for such a task; three would have been better. So happy we didn't try to take them up while they were still paired together; THAT would have been impossible.
We can do anything!