My NodeMCU ESP8266-12E Wi-Fi module is working with 1 smart phone but not working with another smart phone at the same time

I made a nodeMCU ESP8266+12E Wi-Fi module circuit which consists of Input circuit which providing 5v to nodeMCU board and output circuit which Consists of the combination of opto-coupler, transistor and relay. By providing turn ON/OFF commands to nodeMCU board relay will either turn ON/OFF by using same IP address of nodeMCU board and Wi-Fi parameters (said, password) via smartphone's hotspot turning on, nodeMCU ESP8266+12E Wi-Fi module works with one smart phone but not working with another smart phone at the same IP address and Wi-Fi parameters (said, password). Why it is not connecting with other smart phone. The second problem is when this module disconnect with smartphone once due to any reason , there is need to connect again manually with smartphone . . . 3rd , I want to develop a android GUI app for my project can anyone provides me help .