But I don't see why having names that start with the same first letter is such an individuality crusher. Lots of siblings have names that start with the same letter; I know a family where the four daughters all have the same initials, MDL. (Or they did till they all got married.)
Monique Danielle,
Melissa Dee,
Melinda Deanne and
Michelle Dawn. Their parents had the same initials too. It is a bit hokey (maybe a lot hokey.)
But
Savannah and
Sophia are quite different in style, and they certainly don't rhyme. Not like
Savannah and
Samantha, for instance. That would be hokey, and also be hard to distinguish by ear in a crowd or from a distance.