Good use of space in all three images. I especially like the last one...good use of emphasis on the focal point...everyone's looking in that direction and your diagonals are pointing that way too. I do suggest changing the center image a bit...by offsetting the main characters a bit more to the right or try placing them on the left with their shadows going in the same direction. Maybe increase the contrast a bit with the surrounding shadows. Very solid thumbnails, awesome work!
Looks good. Just take away that space ship thing. Doesn't add to the composition and simply is a distraction.
Oh yea... About the 3rd one.