Groups

Can I prevent group members from changing expenses, or set permissions? How do I delete or undelete a group? How do I create a group? How do I edit my friend’s email or phone number? How do I remove a person from a group? How do I split an expense for a couple that is sharing costs? How do I add a new person to a group? How do I join an existing group? Someone was added to the group twice — how can I fix this? Why do I have a non-group expenses group?