There are a few good group email apps on iPad, but the only one that lets you FORWARD an email is "MailShot".
http://Www.iTunes.com/apps/MailShot
It creates contacts in your address book that act as groups, then you can use these contacts directly in Mail or your other apps to forward mail, share attachments etc. (other apps need to use their own mail app)
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<Edited by Host>