Guard is a (sorta) persistent Tor entry, so Guard wont rotate when there are different connections to Tor.
But you can do that if you use Disposable (dispVM) Whonix GW so that each time you open it it will pick a different guard entry, or separate each WS with its own GW.
Note: Choosing different guard each time can be ideal and can be not ideal on the same time depend on the attacks you want to prevent on yourself.
Thus best if you use different GW for each WS