How does Ro speak english? She grew up on an island with no other people.
She was eight or so when she washed up on shore. She probably retained the language but no memories of her past.
In Arianna's Villain Song, she sings, "...just because we tried to kill him and his wife. A little treason, not a lot! He took away our land, which wasn't what we planned. He put us on a pig farm and forgot!" Indeed, the king doesn't seem to remember or recognize Arianna at all. Well, how the hell do you forget that?!
I have the idea that what happened was Arianna's parents tried to kill Peter and Danielle when they were young kids, like four or five. The reason they're referred to as "him and his wife" is because it possibly was an arranged marriage that was already set(it happened!), or Danielle just happened to be playing with him that day and was almost killed as well. Being young, they could have forgotten it after the forty years between then and the movie.