How to make different dynamics in voices

I have a problem with the dynamics - I wrote one one staff a cello solo in the first voice and then in the second and third voice some harmony played by the rest of the section. I would like the soloist to play mezzoforte and the others to play piano or pianissimo. It is possible to put beside the notes two dynamics signs, so when I would print it, every player will understand, but when it is played by MuseScore, I can hear only one dynamics. Also writing the dynamics value for each note haven't helped.
Has anyone an idea, how to solve this situation? (I would need something like "Properties of the voice - dynamics...") Thanks a lot!