Right now when I delete an email from my iPhone I also have to go into my iPad and delete it there too. Is there a way to do it only once?
Is there a way when you delete your emails on your iPhone that they also delete on your iPad?
This is totally dependent on your email carrier, and the type of email account you established. You should have an IMAP, not a POP account to behave as you wish.
Mail settings you might need from your email provider - Apple Support