is there a way to do both pizz and arco at the same time on violln with two different voices and have separate dynamics for each part?

Yes to both questions.

Playing pizz and arco at the same time is relatively easy.

Playing techniques (such as pizz.) can be assigned to a single voice. When I have a divisi where the top plays arco and the bottom plays pizzicato, I use one staff text to assign the playing techniques to the proper voice, such as:

Divisi Arco

Here there are a bunch of notes on the staff

pizz. (this has been moved under the staff).

I use the Divisi Arco text to assign both voices how to play in the "Staff text properties..." dialog. Press the 1 button on a line and select Normal and the 2 button on an different line and select pizzicato. I do nothing with the pizz. to change to pizzicato since it is already done.

I'll explain different dynamics in a separate response.

Changing dynamics is very different than assigning different playing techniques to voices.

What I would do is assign the correct dynamic to voice 2 since you want the dynamic for voice 2 under the staff and this is the default location of a dynamic. I would use staff text for voice 1 dynamics and use ctrl+shift+ the first letter of the dynamic to enter the dynamic. This will use the same symbols as in the dynamics. Note the mf is made up of an m and an f, so you will want to use multiple symbols. This is true of all dynamics.

Next you need to use the selection filter (F6) and select only voice 1 notes. Select the section where you want to apply the dynamic and press the Notes button in the inspector. In the inspector you can either keep the velocity type to offset and make the dynamic for voice 1 an offset of voice 2 (- #'s make it softer) or you can change the velocity to user and assign a velocity for all of the notes.

If you are using crescendos and decrescendos, you will want to make the type offset so both voices are affected since you cannot apply these to a single voice.