Did you try creating a datum curve right on the helical sharp edge as a trajectory and then sweep a cut along it to round the edge? Perhaps you can create this curve as the intersection of two surfaces, adjacent to the edge.
That is hard, because how will the radius end? Shoud it be a full round or just two small ones? The distance between your edges seems to differ.
When you have curves, or create them using the edges, you can create a variable section sweep, with an arc as the section.
Another hint for failing rounds, for example at the end of the round, is to create a tiny cut through the edge so that the round does not go beyond that edge. Fill that gap after your rounds using boundary surfaces.