Hi,
Video is a unusual way to ask questions
1. Voices are shared among the 4 instruments.
What you see on the screen is the number of voices for the instrument you currently edit : #3 in you video.
If you want more voices for I3, you have to reduce the number of voices of other instruments.
More info here :
http://ixox.fr/preenfm2/manual/synth-edit-mode/2. Velocity
If set to zero, volume is not impacted by velocity.
But the different modulation indices can still be.
Search for "v is the amount of modulation that is injected by the velocity of the note you pressed." in the above manual.
3. Maybe your keyboard send program change.
Try to disable program change in the menu.
Search for "Settings" here :
http://ixox.fr/preenfm2/manual/menu-mode/