Why bother with mux and demux? You have an MCU and 5 inputs and 5 outputs.
Do the electrodes give analog signal for strength applied?
If so then read them analog and make the fingers only bend so far?
Whether analog or digital, have the sketch constantly read the sensors and only act on changes.
I guess that the electrodes will some day connect to amputee nerves?
If not or if you want a robot hand for other use, piezo discs do make nice pressure sensors from light touch to hard hits.