It's a very coherent but still kind of unexpected set of sisters.
Portia matches almost perfectly, but I could also see
Paloma. A bit less perfect, but still good:
Petra,
Phoebe,
Pia,
Pomona.
For something a bit less expected, how about:
PallasPalma
PandoraPaulinaParisaPascalePeonyPelagiaPerlaPerpetuaPhilomelPhilomenePilarPolyxena