hey ,i'm a newbie programmer working with a beginner team to carry out a project.heres is the description [on hold]

briefly it consist of a local server(computer) with a database where client(other computers or phones) connected into it can create group chat, play games P2p, do programming battles and more (programmed like a web application).

if have made my research , found some interesting languages (PHP SQL AJAX etc) and also some interesting technologies (frameworks, APIs etc) and so i don't know what language ,and what technology to take (read) that best suits for our projects......please guide on where to start...(study which language,which technology)
how to start(build a server from scratch,learn responsive design?) any security issues ?? if yes , how can i solve them???