How long are the skis? With skins, you have to cut them to the length of the ski, although depending on what brand you can probably adjust them in/out a few inches with the tali clip (at leaston BD STS you could). You could trim the skins to be wall-to-wall on the P4's and get away with using them on the EP's as long as you aren't trying to climb anything really steep, there will still be enough coverage in the middle of the EP's to skin. Icy sidehills could be a problem with that setup, but you aren't planning anything crazy.
Make sure trekkers are compatible with both those bindings first.