Having seen a number of vivas turn out disastrously over the years, here is one thing K would recommend.
The viva is not a foregone conclusion. It is not in the bag. Especially if you haven’t published from your thesis.
Bringing family and friends along on the day to wait outside with balloons saying ‘congratulations’, cake and bubbly is just inviting disaster. if the viva starts turning bad the candidate will be thinking of that and how they are going to save face rather than actually raising their game.
So, don’t invite disaster. Don’t make plans to celebrate afterwards. This just indicates that you’re too cocky. Vivas are to be feared, and for good reason!