Help with photomerge

That does not look like a panorama.  It looks like you panned the shutter set to continuous, and that's not how Photomerge works.  It's done well getting three of the frames in the merged result.  

Try doing it manually.

Load the frames into Photoshop layers.  You can do this with Bridge

In Photoshop, select all the layers and go

Edit > Auto Align layers

followed by

Edit > Auto Blend Layers

Keep the lower two options checked, and try both Panorama and Stack to see which gives best results.

If this still doesn't work, and there's a decent chance that it won't, open the frames with the missing subjects, and use Remove Background in the Properties panel, and place them on the merged image manually.  

It's incredibly easy to do this stuff now because selections are so fast easy and accurate.

Show us the result to let us know how you got on.

Good luck.

It is possible that Photoshop was not able to stitch in the additional people because there is a lot of movement in your photo. As George_F said, check the layer masks in your Layers panel. If the masks are filled with black the pixels on the layer will not be visible.

When it is difficult for Photoshop to stitch the individual images, I have sometimes needed to do it manually. Much more time consuming, of course, but better result.

It's hard to tell, but I think this has something to do with layer masks.  Would you be willing to screenshot the entire screen or the layers panel?