If you want to invite a couple or a family and expect them to RSVP together, we recommend this way to enter your guest information on the Attendee List:

You can only enter one email address in the email field, but you can include recipient's first names or titles in the first name field and family names in the last name field.

If you want an invitee to know they are able to bring a guest, we recommend entering your guest information on the Attendee List in this way:

Your recipient will be able to see "and Guest" included for their invitation when they open their email.

To specify plus ones per guest / invite, go to the Attendee List > and click on the Attendee. Then, select View/Manage to edit the amount of guests that your Attendee can bring.

If you need to collect additional information about each person attending, we recommend that you enable the option "My attendees may bring guests" under Setup > Registration.

Then, you will be able to collect specific information (ie: meal choice, dietary restrictions, t-shirt size, etc.) for each person attending.

To add custom questions, please see support.eventcreate.com/en/articles/1760880-adding-custom-questions-to-registration-rsvp-form