Some are easy, others aren't... I'm not sure I understand the question, don't you know the name of your son? It's the name you gave him at the bris. For a girl, it is possible that she has no Hebrew name, but not a boy.
Sophia is difficult... I would say Sarah, but I can't be sure. There are not always a clear equivalent, like LeonYehudah. It can be uncommon, like my dad Charles -> Chiel -> Yehiel. Or arbitrary, like me Claire -> Rahel. Faye is even more difficult, I have no idea.
By the way, why not ask your rabbi / the rabbi your son studies with?