Hi Chris,
I was married to Richard's cousin Andrew (died 2010), son of Frank Measham Berncastle. Frank did a lot of family research and wrote a pamphlet called "Berncastle Forbears". I have his notes, family tree and some documents. I will look to see what birth/marriage certificates I can find. Josie's grandfather, Richard, would be a good person to talk to. Byll is Richard's sister Rosemary, but they don't really talk to each other - I believe she is in contact with Josie's father, Guy. I don't know about Swiss connection. There is a Berncastle connection in Trier though.
Good luck with the research, maybe Josie can come and look at the stuff I have one day. I live in Hampshire.
Regards
Hilary