The attached zip has two pngs with transparent backgrounds, and a patch that has the pngs wrapped on spheres that are transparent to each other. Can’t sort out how to get the smaller sphere inside the larger.
you need to use the @layer attribute for ordering.
the outer sphere back-faceing shape (@cull_face 2) should be drawn first (@layer 1)
followed by the inner sphere @cull_face 2 – @layer 2
followed by the inner sphere @cull_face 1 – @layer 3
followed by outer sphere @cull_face 1 – @layer 4