Hey! Don't know if you found a solution yet, but I took a look at the Novation Launchkey 25 Mk2 manual.

The drum pads are sending midi data on Channel 10, and the keys will be sent on whichever Channel you select by pressing the two track buttons simultaneously (defaulted to Channel 01).

If you are in Live, put your Drum Rack on its own channel/track, and your piano on its own as well. In the routing section for each track, you will see midi routing. By default Live sets the midi input to All Channels and All Controllers.

On the Drum Rack, click All Channels and select Channel 10. And on the piano, select Channel 01 (or whichever you have manually set on the Launchkey).

And that should stop the overlap! Hope this helps!