Make a playerlist
get the pos of the player.
make a player list.
make checks like ismine, isalive, is player on team, etc.
process player pos through a worldtoscreen and draw to it.
Let me break this into simple steps. (might miss some things)
make a playerlist.
find player pos and process it through worldtoscreen.
draw to pos.
as simple as i can put it. look on github and youll find more info.
I would suggest making a login activity if your not familiar with fire base.
I have made many login activities with fire base and there are plenty of yt tuts.
GL!