Windows on Parallels 10 with 2 out of 3 monitors only
Using UltraMon seems to work fine for me, I've found it in a post on the Parallels Forum:


  I will start the VM with 3 screens, then I use a 3rd party software (UltraMon) and disable the one display so that my VM uses two screens running Windows 7 and my MacOS uses the one.