There’s no single right way to select examiners. There’s no best criteria for deciding whether you should have you supervisor at your viva. I can think of many options for planning out and completing viva prep. I have a lot of suggestions for how someone might build their confidence before their viva – but I don’t know the best one to suggest to you offhand. And, of course, there are many different questions that can be asked at the viva, many approaches that your examiners can take, endless variety of situations on the day.
There are so many aspects of the viva that have lots of possibilities and yet, ultimately, there’s only one way you succeed: you do the research, grow as a researcher, write your thesis, submit it, then prepare for and pass your viva.
It’s the only way to get it done.