I agree with all of this. It's definitely better to use a full name rather than a nickname.
Penny is especially childish.
suggestions:
Jessie -
Jesenia, Jesperine,
Penny -
Penelope,
Peninnah,
Sam - I've heard of
Simon's going by
Sam. Also
Samir, or
Salamon.
Sally -
Salma,
Salome,
Salvatrice