Pia is so much more modern than
Paula, which is incredibly dated. I agree with you, the sibset is a bit mismatched. What bothers me is that the names are so different in terms of classiness;
Pia is
Pia Zadora to me, and
Paula is the trashy fake-blond fake-boobs hairdresser down the road.
I think
Paola,
Piera, Peri,
Poppy,
Penny,
Perla,
Polly, or a similar name would be a better fit.