Engine running on two cylinders but has good spark on all four.

A four-cylinder engine has four spark plugs. An important part of the power-generating process, each spark plug is responsible for igniting the fuel and air mixture inside of its cylinder. At the beginning of a stroke, a piston moves downward in its cylinder, drawing in a precise mixture of gas and air. After reaching the bottom, the piston moves back up, heavily compressing the mixture. Once it reaches the top, the spark plug ignites the mixture, and the explosion forces the piston down into the cylinder. This mechanical movement is harnessed and used to power the vehicle. Some large engines may have two spark plugs per cylinder to ensure that complete combustion is achieved and maximum power is generated.

Is it a 4 cylinder engine, and all four cylinders are misfiring?

Misfires will set a code when the computer senses a lag in power output from a cylinder, based on the input from the crank position sensor. Misfires are usually caused from a loss or a problem with gas, spark, or compression-one of those three is wrong for a misfire to occur. New coils and plugs, so probably not a spark problem-unless the spark timing is wrong-let's leave that for now. You should have the fuel pressure tested, and see if pressure is as specified. If pressure is low, and you have new filter, probably a weak pump.

Check cylinder compression as a last resort. Your lowest reading cylinder should be within 75% of the highest reading cylinder. A compression test is a good indicator of the internal health of the engine, the higher the compression, the more power output from that cylinder. But it should be even and balanced, lowest should be within 75% of the highest reading.

So, gas, spark, or compression?

You mean without taking it to a shop for repairs, or at least some diagnosing? Check for spark on all four cylinders. If two do not have a spark, the problem is in your ignition system. Possibly the ignition coil for the two not working.
If all four spark plug wires do have spark, it could be a fueling problem to the cylinders not firing, or it could be an internal mechanical problem in the engine. Then you would need professional help.
Google or watch a vid on you-tube for how to check for spark, if you are not sure.

There are four things required for an engine to run: air, fuel, compression and properly timed spark. If you have fuel and timed spark, the only two variables are air and compression. Air is not the likely problem, and compression should be good unless you blew a head gasket or the rings in all four cylinders. How did you determine that you have fuel and spark? Those are the two most likely problem areas.

see if you have spark at all four plugs. If you have good engine compression, then you might have a bad injector. While running, I unplug one injector wire harness at a time, and the cylinder that doesn't change, has an issue.

might be something as simple as changing the spark plug or related wire, could also be damadge to the valve train or piston and cylinder bore

if this is a four cylinder engine it will be the one further from the fan belt,check the spark plug but it also can be the ignition coil for that cylinder.

If it's a four cylinder it has four spark plugs.
If it's a six cylinder (V-6) then it has six spark plugs.
Hope this was very helpful.

you may have sticking valve or a weak or broken valve spring sometimes an exhaust valve rotator , it maybe that the # 1 cylinder exhaust valve is slightly bent and when it rotates to a certain spot it hangs slightly... requires inspection for confirmation, due a compression test or a cylinder leakdown % test...

Subaru engines (including Legacy and engines of many other automobiles, GM, etc.) have returned to so-called wasted spark ignition systems since advent of the electronic distributor-less ignition (having been used historically in early engines with magneto ignitions). With this approach, the ignition systems are less expensive and usually quite reliable. At the same time, however, a shorted spark plug (cracked or carbon clogged, etc.) (or bad ignition spark plug wire) grounds both the ignition spark and the false spark being used. This means that it also grounds the corresponding respective ignition spark of the other 180 degree out of phase cylinder (that uses the same the same coil because the spark current is connected to the spark plugs of two cylinders). Since such a defect allows more current to flow in the spark coil to two plugs when the resistance of the spark plug gap disappears due to a cracked plug, etc, it seems likely to hasten coil burn out if the spark plug/plug wire defect is not corrected before installing the new spark coil.

To explain further, wasted spark means that when a cylinder is ready to fire, it gets a spark to its spark plug while part of the spark (from the same coil and current) as a sort of copy is also sent to another cyclinder at the same time but when the piston in that cylinder is exhausting its ignited gases 180 degrees out of phase from when its spark is needed. When the second cylinder is ready to fire and receives its "spark, the first cyclinder the also receivesa "wasted" spark "copy" of the one needed by the second cylinder. Economy is achieved in manufacture because otherwise electronics would have to turn on and off four different spark coils to distribute four different sparks as needed to the four cylinders. With wasted sparks (which are cheap), because the spark current of one coil is connected (internally in the ignition coil unit) to two cylinders that are in the same position but 180 degrees out of phase in firing, the system can turn on and off two spark coils twice as fast with half the electronics and fire two cylinders that are 180 degrees out of phase. A four cylinder engine thus uses only two coils, a six cylinder engine, three coils, etc., in a wasted spark system.