You need SmartThings and webCore. Do you have those? If so, create a virtual switch in SmartThings. Next, go to IFTTT and add your SmartThings and Blink accounts to link them to IFTTT. In IFTTT, make an activity which arms/disarms based on the status of that virtual switch. Once your phones are added to SmartThings as presence sensors, build a webcore piston which, when both switch to away, the virtual switch above is armed. When ONE switches to present, have the piston disarm via the virtual switch.