You can install our site as a web app on your iOS device by utilizing the Add to Home Screen feature in Safari. Please see this thread for more details on this.
Note: This feature may not be available in some browsers.
You can do it either way. We both use the same login/account on the app. Or one of you can get a separate Tesla account and become an authorized user. An authorized user sees pretty much everything in the app the same as the owner.