you can increase your glossy reflections subdivisions in your material. Default is 8, you might use something like 32 Also perhaps increase your light source subdivisions. Either way, make sure you are getting enough samples so the reflections get cleaner.

sure, it's possible if you're on the same computer. If you only have one license you can only use one computer at a time. You may also be able to set processor affinity so you reserve some cores of one session, and other cores for the other session. (since vray uses all available cores to render, it may be pretty slow to run two renderings at the same time.)