Updates as of season 5, episode 15:

Casey -- SEE... or wait... she seems caregiverish?

Evan -- LSE or LIE

Cappy -- IEE

Rusty -- EII

Rebecca Logan -- ESI?

Ashleigh -- ESE

Frannie -- EIE

Katherine -- LSE (and duality with Rusty in this episode!)

Natalie -- SLE?

Calvin -- still not sure