Multiplayer change of control script

I'm trying to set up a multiplayer game where the host is a RTS style commander who creates and runs units. Each unit is a squad of five soldiers centered around a point. Other players can join in an take control of one of these squads. They would spawn into one of the central points of a squad and then control it. For now the squad will just continue to follow the central point which is the new player.

What I need help with setting up the network so that when people join they go into one of the squads and take control of it. How do I change control of the squad from one player to the spawning player? How do I set the spawn point randomly to one of the squads?