If the images of the suits of the astronauts are static and you only need to put some videos inside the helmet which you can mask with either polygon tool or wand tool etc than its pretty simple process of using merge nodes to merge videos of the faces on top and use masks to mask them out so they fit inside the helmet. You can use transform tools to scale and position the videos where they need to be.
You can also use one multi merge node and add the two videos and use one or two combined masks as I've done here for illustration purpose. Since the images insides the helmets were just solid color I used wand tool (similar to magic wand in Photoshop) and I combined two wand tools to give me mask of the inside of the helmet and one multi-merge node to combine two videos and mask them. That's it.
Like I said you can use merge node per video or one multi merge node, same thing. You can use polygon or B.spline or any other tool to mask the inside of the helmet shape and apply the mask (blue input) to merge nodes or one multi merge node.

- sshot-960.jpg (49.76 KiB) Viewed 921 times

- sshot-961.jpg (240.97 KiB) Viewed 921 times