Re: how to address in email
As with everything, context matters.
Tell me more about the situation, why you are sending one e-mail to five people instead of five e-mails to one person each, whether one person is the "to" recipient and the others are "cc" recipients, whether they are junior to you or senior, whether you are asking them for help or fulfilling their request, etc. etc.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.