If you put a small resistor (10mOhm) between every pin1 and source gnd, you get a small voltage on pin1 wich will reduce the voltage depending on the current ever so slightly (max 10 mV) which is enough to devide the current pretty equally amongst the 1117 ICs. But you have to leave room for margins to not overdraw a single IC. Better is to use a 3A regulator, switching is more energy efficient than linear.