It’s good to know about what your examiners do but you don’t have to know all about them to be prepared.
At a minimum, if you don’t know much about them you can read a few of their recent papers in the weeks leading up to the viva. Then you can get a sense of who they are, what they do and what they spend their research time on.
It could be you already know this before you submit your thesis. If their work has been part of the background for your research then you might be more familiar than I’ve outlined above – and of course that’s fine too!
And similarly, it’s enough for them to be familiar with your area of research if it doesn’t correspond to everything they know and do – your examiners don’t need to be experts in your thesis focus in order to be good examiners for you.