You can share your HomeKit configuration with all your iOS devices that are set up using the same Apple ID. On top of that, HomeKit allows guest access. Use it for family members and friends who use a different Apple ID on their iOS devices. Note that guests do have full access to view all the values of your HomeKit-enabled devices and can even control them — such as Eve Energy. Guests are not allowed to edit your HomeKit configuration or invite other guests.
HomeKit accessories, including Elgato Eve accessories, are setup with an iOS device — for example, your iPhone. To share your Eve accessories with other devices such as your iPad, you can set up other iOS devices using the same Apple ID as the master iOS device, and iCloud will sync the HomeKit setup across all of them.