The simplest way I found:
Load both photos into Photoshop.
Click on the Move icon (the four arrows in all directions).
Right-click on the tab of one photo and select Move to New Window. It will minimize slightly.
Drag that photo into the other photo. That creates two layers in the other photo’s frame with full opacity.
Reduce the opacity of each layer so you can see both layers for positioning.
Drag each layer into the position you like, and select the opacities. Full opacity will bring back the original for a layer, and 50% or so will make that layer a ghost image.
Select both layers in the sidebar.
Select Edit/Auto-Blend Layers. You may want to have Seamless checked.
If the settings look good, click Okay, and you should get the blending you want.
You may need to experiment a bit with the steps, but at this point you can do whatever other processing you want, and save.