This is due to the limitation of latest Bluetooth 4.0/4.2 LE technology, which only allows the Sesame to be connected by one master device at the same time. Just like that an Apple Magic Mouse can only be connected by one Mac computer at the same time.
So please ask your family members/ friends to close their Sesame app if they are not using. Thanks.
By the way, Sesame with the latest Software 2016-8-29 will stop any idle Bluetooth connection which is idling for over one minute, so you always have a chance to get back the control.