FIXAMO - Ultimate Mixamo Blender addon

INSTALLATION ----

Go to preferences > Addons > Install and install the script in the downloaded zip or 

you may just install the zip without extracting

At the side of the viewport where your addon panels are you will find a tab Called TOOL! Click that and you will see 

a button called "FIX" click your armature  and click fix!  You will notice your armature is renamed to prevent the next armature import to conflict!

This needs to be done for both armatures :) Done! now just copy the keyframes from one to another and past them at the end 

or any place after if you space it a few frames after the first animation it blends incredibly well

TO LOOP ANIMATIONS ---  Just click fix on the armature and copy and paste the frames back in at the end!