I would check firing order on coil packs one more time, yes I know you checked it already, me too, but I still get it reversed, lol
Cam position sensor is for fuel injectors, spark is based on CKP(crank position) sensor, behind the main crank pulley, it isn't adjustable, and if it isn't working then you would have no spark(or fuel) at all.
What happens if you add fuel manually to the intake?
Reads like you have spark
Do you hear the fuel pump come on for 2 seconds when key is turned on?
You can't really setup timing chain 180 out, like a distributor, but if you did remove timing chain and re-installed you could have miss aligned it, but that would usually cause valves to hit pistons which wouldn't sound like a backfire.
Melting pistons is from pre-detonation, pinging/knocking, I assume you could hear this prior to the loss of compression?
So there is an underlying problem that caused this.
Lean fuel mix can cause it, perhaps an intake gasket leak near #1/#2.
Low fuel pressure at #1/#2 injectors
Carbon build up in #1/#2 from running too rich over time, sticking injectors
EGR(exhaust gas recirculation, cools cylinders) system not working, but I would expect all cylinders to show signs of pinging
Too much spark advance, bad ICM(ignition control module) in PCM, but that should have effected all cylinders.
Did any other pistons have pitting from pinging?