iOS files are your iPhone. Looks like you're backing up your entire phone to your laptop (??).but showing ~95G for iOS files
Yes, Dropbox "syncs" files from your computer to their cloud storage, i.e. they keep a copy. You can turn on "online only" access on the computer and it will remove them from your computer but will keep links in Finder that will make it appear those files are still there.Documents: I try to upload the big ones to Dropbox, but still take up space...