For a pure overlay you should be making
a single datasource from your two ones.
Same as if one try to map two set of Marks
using two different Lat/Lon pairs of coordinates
which comes initially from different sources.
I could play with your Point data a bit
and would offer a partial "solution" --
those using Continuous Bins on Dual Axis.
Please find the attached.
Notice that the view comes from a single source.
I included your Points datasource as a reference.
Overlay_YF.twbx 1.3 MB