Common Ground
A small part of viva prep is making sure that you know who your examiners are and what they do.
This does not mean that you need to become an expert in everything they do. As part of viva prep, unless you really know a lot about their work already, take time to read their most recent papers. Look for recurring ideas, themes, questions and methods. Look at their staff pages for their research interests.
Try to explore the common ground that your research shares. Look for the connections between what you do and how you do what you do. If you need to, take a little time to understand any differences between your research.
Again: a small part of viva prep is knowing who your examiners are and what they do. It helps, but make sure you spend your time well.