Hi, Welcome to the Forum Nils!
Here are all important links:
http://lmms.io/forum/viewtopic.php?f=1&t=4740
-A few rules and useful forum instructions
LMMS does not have an option for that. Some MIDI-kb do allow to split the keys, but i do not know if mpk mini mk2 can do that. Read your manual.program a separate instrument for the music keys and the drum pads.