I somewhat like
Pearl.
It does sound like they were twins but then again, my grandmother birthed 13 kids. 11 of whom had ridiculously matchy names. (Every -'Arry' name you can possibly think about;
Harry,
Larry,
Barry,
Parry (
Paul)
Mary,
Sherri,
Carrie etc. Not joking. Many of them went by a nicknames; unassociated with their name. Personally, I don't think its such a wise decision to have sibling names be so matchy. Twins or non-twins.
Anyways, Prela &
Pearl do come off as twin names but at least they aren't too matchy. (Well they are matchy but not at an obnoxious level)At least its not perla &
Pearl