As pinned above, I know that Acco's twitter is @accobin and Kumiko's is @kumikon_drum . Japanese staff is @chat_staff and whoever is officially in charge of informing English speaking fans is @chatmonchy_en
However, does Eriko have a twitter account? I know there is @hashimotoeriko but I really doubt it's her as @accobin and @kumikon_drum don't follow it and never @ that account in their tweets featuring Eriko.
Is Eriko just not a Twitter fan? :)
At this stage she doens't appear to have a twitter acccount. She does however occasionally tweet using the staff or kumiko or akko's account.