How can i edit the after effects files in photoshop?

You could start by creating all your AE animation based on a single PSD, but ultimately that's very limiting because you have to avoid converting text to editable text in AE and otehr such stuff or else you never could be sure the changes carry over correctly. in the long run the smart thing to do would be to create some idiot-proof AE projects and sell your client some AE training on how to work with the templates you create for them.

Mylenium

You can import movies into PS but not AE project files.

You can export your AE layers as a layered PS file - Composition>Save As> Photoshop Layers.