Well, I like both about equally. But
Corinna and
Serena do not rhyme, imo. I would assume
Corinna was cor-INN-ah and
Serena was seh-REE-nah. I guess you're saying
Corinna like I say
Corrina, though.
However, how are you pronouncing
Helena? If it's heh-LEE-nah, please don't use it as a sibling to either
Corinna or
Serena. Way too rhyme-y! Helen-ah would probably sound best as a sister to either one, but even heh-LAY-nah is a bit too similar in sound, IMO. Also
Helena and
Serena, even if they don't rhyme, look too similar for sisters to me, too. :-/