Hi Ramesh,
I concur with Eric's answer to your second question, so I'll address your first question:
Blue Prism does not support running two or more different versions of Blue Prism on the same machine or environment, even if you're connecting to different databases. Blue Prism components are not designed nor tested to work with other different-versioned Blue Prism components (i.e. a v7 AppServer with v6.6 Resources/Clients per your example), so this would be an unsupported configuration.