If your characters being online is part of the story, what do they canonically go by on the web? If not, what usernames would your characters choose if they were in the modern, internet-using world?
I've only come up with usernames for 3 of my characters; they haven't shown up yet, but they will in the future XD
Saku (a.k.a Horizon Tally)
A punny username befitting his sense of humour
Dolly (a.k.a The Expositor)
She helps people explain their opinions on the internet
Emma (a.k.a 9gramsofpersonality)
She was very into personality tests when she was younger