Really these do belong in the art forums but what I will say is that if you want them to be really a set look at the last two and use them as a guide.

They were more obviously designed to match each other (look at how the droids and Yoda are in almost the same positions, how the gunship and the Jedi fighter are in almost the same position).

I'd get a ruler out and connect this points of similarity together and adjust the TPM poster accordingly. I'd also reduce Anakin to match Fett (or enlarge Fett to match Anakin) and remove the lens-flare trailing along the bottom border of TPM by fading it before it enters the same area as the title.

Having the flare dip so low is very busy and spoils the balance of the piece.

It might even be worth sampling an image of Yoda for TPM poster to replace Mace (Mace is a boring character anyway) in the correct position and use a different image of the droids positioned in the same area as in the other two so you see the evolution of Threepio throughout the trilogy.

I'd replace mean green Palpatine with an image of Darth Maul (aren't we supposed to believe he is a good guy in episode one?).