Invasion S02-Ep01 - WTF?

Just watching the first 25min...
Did the aliens just go from 'undestructable' to 'easily defeatable with fire'??
This woman in the beginning easily killed like 10 of them with no trouble - just throwing molocov-cocktails on them, or just igniting a little explosion ('a trap') when they run mindlessly towards her, easy peasy.
Just have every civilian make molotov cocktails. They run 1 meter through fire and just die easily. Alcohol, lighters, some pieces of cloth is all you need to kill them? And that's just as a single civilian.
Military can hand out flamethrowers, all kinds of stuff

The Family (mother with 2 kids) drives around.. with a unique super-weapon that kills the Aliens supergreatly. And what are they doing?
Do they give it to the military so they analyse it and can win the war and save humanity?
Nah, better not tell anyone about it and drive around frantically towards 'north, where no people are'.
WTF?
Am i missing something? I am not smart but these two things seem so stupid to me i kinda want to ask screenwriters 'wtf why'