The current UI does not provide a clear path for event registrars when they want to register a new family members or guests. Here is what the screen may look like when you leverage these settings:

Here are the issues I see with this design: 

1. If they want to add a new family member, it's not immediately obvious how they would go about doing that. The only path forward is to change the dropdown to have a blank value by clicking the X which only appears on hover.   Selecting a blank value is not an intuitive way of indicating that you want to add a new person. 

2. If they want to add a guest, the only path forward is to change the dropdown to a blank value and then to change the "is in the same immediate family as" to "none of the above."  After you do this, the dropdown label still read "Family Member to register," this is confusing.

Here is a suggestion for how we might move forward using no blank values and only one dropdown input, eliminating the need for the "is in the same immediate family as" selection altogether. 

There may be some debate about whether "New Family Member" and "Guest" are exactly the right terms here, could be configurable.  With these new options in place, it would be immediately clear to registrars how to add new people while registering. 

This is important because users are consistently confused when family members are not listed, e.g. new babies, and sometimes change their own information to reflect that of the child being registered.