Does a 4 pin smd crystal need external capacitors to work properly?
These parts are crystals that can be used with typical microcontrollers that have a built-in Pierce oscillator, and thus require the rated external load capacitance in order to oscillate at the rated frequency.
So yes, external capacitors are needed as usual for crystals. The extra two pins are just to ground the metal lid.
And no, the rated load capacitance does not mean the value of the capacitors. It is the total capacitance as seen by the crystal, which includes the capacitors, PCB wire capacitance, MCU IO pin capacitance and other stray capacitances. The ECS part is rated for 12pF load capacitance, so two 24pF capacitors would give it 12pF of load if no other capacitances are considered. But the capacitors must have smaller value due to the other stray capacitances.16pF capacitors would be used to give 8pF load if the stray capacitances are approximated to be 4pF.