joshdefreitas さん、
You are welcome.
Your sir name should be フレイタス.
slimispriceless さん、
Unfortunately, we don’t have any rules for that.
Some foreign words were written in katakana by our ancestors and they became social custom.
However, especially regarding names, you can choose katakana writing yourself.
Xavier should be ザビア or ザヴィア.
You can choose one of them.
Yuki 由紀
Team JapanesePod101.com