You can create middle curve between two curves or points using Middle Curve.
To create middle curve:
Click Middle Curve (Curve toolbar) or click Geometry, Curve, Middle Curve.
Middle curve locates between two selected curves. You can also create a middle curve between a curve and a point, or even create a middle point between two selected points. "Merge Wire to Edge" will firstly merge the selected curves into one curve.
a. Two source curves and one point. b. Middle curve between two source curves. c. Middle curve between one source curve and one source point.