Walls and Ceilings - using a foldable ladder

I guess this the right place to ask this question. I've got a foldable Wagner Multi-Master ladder I bought at Home Depot. I am working on the project where I remove all popcorn ceiling in my house and the toughest place is above the stairs, that's why I bought that ladder - hoping it will help to reach farther. Stairs are 8' high and 14' long and I can't even imagine what can I extend over that long of the span that would not sag or be stable enough that I wouldn't break my knack. I also learned that even when the ladder is folded in the most weird way and looks like I could reach the ceiling, ladder's instructions say that you should not stand on or higher then second step from the top. In fact ladder seems to be unstable and does not provide a good foothold. Please help with suggestions. Thanks.

What I do is use 2 ladders, one standing nearly straight up and near the bottom step (but on the steps). The second is laid flat on the second floor and extends into the the rungs of the first ladder. Take scrap lumber and lay them on the horizontal ladder and walk on them.

Thanks much for advice, I hope it works for me
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