At this point dropinchat.com does not support sending messages to more than one user. However, we do plan to add that feature as our team has time.

The documentation on dropinchat.com mentions "groups" as a set of users which are allowed to see one another and message back and forth. Our team thinks this use case might be helpful, for example, for a website administrator to limiting communication between members on a given organizational team or individuals in a certain building, etc.