All Form options (like Allow Guests to Bring Plus Ones) should not be active.
This setting should be set by the event organizer, not Splash.
The page’s RSVP Form properties shouldn’t be set by default. But if they are, you can just click the Form tab in your event's toolbar. Make sure that the options Allow Guests to Bring Plus Ones, Allow Invitees to RSVP "No," Limit One RSVP response per email, and Include Captcha Human Verification are left unchecked. Once you’re done, hit the Save button at the top right.