Setting up a reusable group email list in Gmail

put the label in Bcc instead of To if the people on the list don't all know each other. then nobody sees everyone else's address, and you don't get a reply-all storm.

It's done in Google Contacts, not Gmail itself. Select the people, use the label button to make a new label (call it something like family), and save. Then when you write an email, type the label name in the To box and it fills in everyone. Anyone not in your contacts yet has to be added as a contact first or they won't show up to select.