If your plugin hasn't appeared in Adobe Photoshop Elements, please do the following:
Copy the files with the ending _64.8bf from the AKVIS folder into the Plugins folder of Photoshop Elements.
For example, to add the Sketch plugin:
Copy Sketch_64.8bf from the AKVIS folder C:\Program Files (x86)\AKVIS\Sketch
into the Plug-ins folder of Photoshop Elements:
Then re-open Photoshop Elements and check how the plugin works: Filter-->AKVIS-->Sketch.