Can I use the same email for two players when I register my son and daughter?

You can add information to the email address to make it unique. For example: 

The Son has the email of ‘thesmiths@njgt.com’ 

The Daughter could use the email ‘thesmiths+1@njgt.com’ 

Everything after the + sign is viewed as additional information via Golf Genius & that way both players can have the same email address, but remain unique in the system.