Homefront: The Revolution

So I thought I'd add my two cents because I got this pretty easily.

The first opportunity you have to face off against a bunch of bandits is during the first mission, right after Jill says they're holding off a bunch of 90 and you have to melee a pallet to proceed. This is also the same area you must stealth through for the Unbreakable achievement.

Up to this point, if you've been keeping an eye out for materials at all, you should have enough materials to craft one molotov for a total of two when combined with the one you begin the DLC with. After continuing through the tunnel, you'll come across an area with a guy complaining it's cold with a school bus in the middle of the room. Directly to the right on a table when you enter is more crafting materials to make another molotov for a total of three. Continue forward and stealth kill the guy directly ahead of you, and the table has was standing at has more propellant to get you a total of 4 molotovs. Now all you need is the slightest bit of luck and/or skill to kill two guys with one of the molotovs.

What I decided to do was turn right directly from the table you collected the final propellant tank from and head onto the next platform. There will be an enemy wandering around there, and you want him to spot you just before you roast him. From the north, every other enemy in the area will file neatly toward you down the platform for some easy molotov kills. If you mess up, just restart the checkpoint.

Since this is also the area you must take no damage for another achievement, I recommend restarting from checkpoint to get that achievement done right afterward before you proceed with the campaign.

Since I have just played through the DLC without getting this achievement on my first run, I will give you some tips if you want to do it in one run.

The DLC consists of three missions, this achievement can only be achieved in the first and second mission. Try to look around carefully to get the ingredients to make molotovs. I've only been able to find enough to make three molotovs (plus one you've been given from the start). That would require you to hit two bandits with one molotov and hit one bandit with each of the other molotovs.

There are only three sections where you fight bandits. Right at the start of the DLC, underground and in the bandit camp (which is also underground). Until you reach the bandit camp, you likely only have one molotov. In the section before the camp, there are two bandits on the right hand side looking at another car. Perfect opportunity to set them on fire. Then just kill the rest as this doesn't void any other achievements.
It's pretty hard to get the stealth kill achievement in that section, so do that later in the camp.

Get more ingredients on the way (especially slightly before the camp and in the camp itself). Once the car in the camp is destroyed and everyone else is dead (see the other solution how to not get hit), there will be three bandits as reinforcements (at least on the lowest difficulty).
Just wait in the room with the switch until they come through the door and fry them with your (hopefuly) three remaining molotovs.

If you want to do it in two runs, I've got good news. The amount of kills carry over.
Right at the beginning of the DLC, you will be in a bandit fight and you'll already have one molotov in your inventory. Get your remaining kill/kills there.

However farming this achievement by checkpoint reloading does not work. You'd need to hit the first checkpoint after the first bandit fight, then quit the game and restart the DLC.