What you need to do is take 2 identical photos of the scene, dont move the camera, do them straight after each other, ensure the lighting does not change.
Do one photo without persons, and one with persons.
Then in photoshop mask around the photo of the person so remove the background. You have to make the background (layer) into a layer to get the transparency.
Select whole of the photo with no persons, and paste/insert it into the same document as the previous photo. Ensure it is at a lower layer level beneath the original.
Now.. this is the ghost part. On the upper layer with the masked person, decrease its transparency untill it looks right. Also add some GAUSSIAN BLUR to the layer (as much as look right). Maybe even a little GLOW via the Layer STYLES (but remember the mask may hide it), remeber to have to correct colour of the glow and tweak it etc..).
Here’s another hint yall might find useful. First, you take the picture of the cemetary, and keep it in an open window. Make sure there are no people on it. Just the scenery. Then take a picture of the people you want in it. Cut them out manually, or with the magic wand (wichever you prefer). Then, use any selection tool to select the people/person, and drag them on top of the cemetary picture. Then, as blending effect, you can select Lighten at general blending, or put a slightly transluctant (No idea how to spell that word) white color overlay on it. Also, if you want, you can put a nice glow around them.
Go with all of the above suggestions, but on the layer of the person, decrease the opacity to make the person transparent. I like the glow idea!
San…
Before getting too deep into this project, have you considered that it might be creepy and weird? You could do it tastefully, I suppose, but a certain percentage of those who see it will still think "ewww."