Don't put two spawns in the same area, just put one. Unless there is a setting that says spawn away from team, thats probably the best you can do.
Not putting the spawn points close to each other won't work too well. You'll still have 1 team spawn first spawn in one area of the map and the other team in another area. You'll have to change the team settings of the spawn points. If 2 points are close to each other then set one to defender's and one to attackers.
First of all, why would you even want to make a map like this... and second of all, maybe you could make people stronger, with their backs to a wall, or spawn in closed shield door boxes. Or people could spawn on mancannons/grav lifts, making it harder for people to spawn kill, and letting the spawner get oriented.