Volume of certain instruments and velocity on dynamics

So for whatever reason some instruments and voices are louder than others. Like if I create a score the is a vocal piece with piano, the piano will overpower the voice and I can barely hear it. Another example is that the base volume for Alto voices is extremely quiet and the base volume for Soprano voices are much louder than the Alto voices. There is also no way to adjust the velocity on the dynamics. So what is piano (soft) for the Piano is completely different than the piano (soft) for the Voices causing the Piano to overpower the Voices. Please fix this.