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.
Similar to using your HomeKit configuration on your other iOS devices, inviting guests requires iCloud and iCloud keychain enabled on both your and your guests’ iOS devices. More technical information can be found here: Technical Background
To invite a guest, you need the Apple ID they are using. Select “Settings” in Eve, then tap on “Guest Access.” Eve then checks if all HomeKit-enabled devices are within range of your iPhone. These devices will then be informed that there is another Apple ID allowed to view their values and control them.
The next step is to enter your guest’s Apple ID (email address). Your guest will receive a push notification, which they can accept or decline. If they accept the invitation, they can choose to control their own device or the one they’ve been invited to. They will then be able to see and control all the devices in the host’s home.
The inviting user may revoke the invitation later via the Eve settings; the invited person can revoke the invitation on the iOS device by navigating to Settings > HomeKit.