Are two people able to edit and publish different pages on a Voice website at the same time?
If not, as I know applications are slightly different from standard pages, is it possible for one person to update a standard page while another updates an application (eg. Events Calendar)?
There's no problem at all with multiple users editing the site at the same time.
However, if you both edited the exact same page at the same time then one person's changes would overwrite the other person's changes (Voice isn't clever enough to support concurrent editing of the same page). But other than that you shouldn't run into any problems!