Just a heads up, that these are not very safe. Each step/rung is only held up by the grip of the screws in the hinges. A safer design would have each step / rung resting on top of some kind of block that is supporting the user's weight.
Well, the hinges on the right side are both screwed and glued. Each hinge has 4 + 4 screws, good thick screws that reach almost to the other side of the stair. The glue is construction glue. On the left side, the hinges are on the bottom of the step so it's naturally stronger. If heavy things are going up we can just stay left. The stairs are mostly just used by my daughter who is small, so I think it should be good.
True. Or, possibly thru bolt the hinges to the rails and rungs using the largest washers you can get away. That could help some. Looking at the way they fold, support blocks under the rungs may work fine on the right rail, while blocks on the left, I imagine, will get in the way of the folding. They look like a great solution.