As a set, the theme is too obvious for my liking, but each to their own.
Individually the only one that I would actually use is
Pearl.
Ruby is too cutesy/childish in vibe to me,
Olive is too strongly associated with the fruit (or colour),
Heather is dated to the 80s/90s (or 70s/80s) and
Myrtle is quite ugly.
Ivy is ok.
Without repeating any initials I would name a brother
Jasper and another sister
Violet.