Using only passive location, and hourly update, Where's My Family uses minimal battery meaning you can safely leave it running at all times. Because of this, there is often a delay when updating the map, and the location can be fairly rough. It's accurate enough to know if your loved one has moved from Cambodia to Vietnam, but won't tell you if they're on their way home from the shops right now.
You stay in control of your location data. To use Where's My Family, set up one single private Twitter account that you control. Each person you wish to share locations with can login to the app using that Twitter account. Only people you give access to will be able to see your location history.