Just a guess but I wonder if this could have anything to do with a natural release of phosphine from organic breakdown in the soil. Such a large release would be extremely rare, but it would automatically self-ignite, especially if it was able to build up inside the enclosed area of a home, and would explain many of the accompanying toxic effects. The combustion of phosphine can give off a luminescent white glow.
The problem I see with that is that there was no sign of heat being produced. Also, they were in a building and all doors and windows were closed at the time. So it seems unlikely that they could quickly receive a large dose of gas at the same time it ignites outside. And nothing was burned. That is a great suggestion but it seems to have a lot of conflicts with the reported facts. Also, I don't see the loss of hair as a side effect of exposure. And the fact that only one side of their bodies was heavily affected.
Combustion of some of these types of gases can take place at much lower temperatures than regular flames. Here's one video example of this, a man is briefly burning another compound called carbon disulfide in his hand. Phosphine can burn at even much lower temperatures than carbon disulfide. (They say it burns at 100°F. For a flame, that's nothing, you wouldn't even feel the heat most likely. Carbon disulfide is 600°F and you could still manage to put your hand in the flame for 4 or 5 seconds without getting burned. A candle, for comparison, burns at 1,500 °F.) When even a small amount of white phosphorous burns, it gives off a lot of light. And it's a much brighter white light than the regular flames when organic compounds burn. Again, phosphine burning in air would behave very differently from the normal type of fires people are used to. They also reported hearing a loud humming sound. That's not unusual either. It could have been rapidly coming up through a crack in the earth, and that could have made noise like a pipe organ. There is another chemistry demonstration called the "Barking Dog reaction" where two gases are ignited in a narrow column and it gives off a strange sound, very much like a deep low-pitch humming. It's also a lower temperature type of combustion reaction. According to your story, there isn't any mention of it igniting outside. It most likely could have ended up affecting the trees through the roots. One of the immediate effects of exposure to phosphine is queasiness and vomiting. Hair loss is a longer term effect. The fact that only one side of their bodies was affected probably may have to do with that being the side facing the flames. Phosphine tends to immediately react with air, so it would not have been able to build up to more than very low levels. However, when a gush of phosphine suddenly shot out of the ground, that caused the flames. To explain it to you this way, the phosphine exposure that they received on one side of their body wasn't able to reach the other side of their body before being completely oxidized by the air. It's actually a little more complicated than that. If the gas was incompletely burning, it could be forming other solid compounds which have similar toxicity to the gas. These compounds would have been in the smoke, and are just a bit slower to oxidize. So if these tiny particles were being ejected out of the flames, it would only be the side of their body receiving it that would be subject to the toxicity. The combustion flame of a compound like phosphine could also be very diffuse, like a glowing cloud. Very likely nothing would have been burned. Reaction of phosphine with air is very different than the type of combustion you're used to. There's something called the Lower flammable limit which is the minimum percentage of flammable compound in the air that's required to sustain combustion. For phosphine, that number is extremely low, 1 or 2 percent. That means the flame could be very diffuse, it probably wouldn't even look like flames. Wood doesn't even begin to char until 250°F, and the flame temperature would have to be much hotter than that if it was only for a very short duration. So it's no surprise there wasn't any signs of fire.
The article described the home as a hut, so there may have a dirt or clay floor. If the flame was coming out of the ground, there might only have been transient flame contact with the walls or ceiling. With a flame temperature under 250°F, or even if it had been 600°F, likely there would have been no signs of charring or blackening. The rain from the storm may have had something to do with driving the gas out of the ground.
I need to take some time to read your post and stew on it. I just wanted to mention a favorite explanation of many, that being ball lightning. We know it can be highly energetic. In one case, ball lightning "exploded" on impact and destroyed a roof, on a house in Japan. We still don't have model for ball lightning. So the idea that it could produce some kind of highly energetic electromagnetic event, even perhaps that could burn people, isn't beyond imagination or into the realm of UFOs as an explanation. It is reasonably conceivable. But to my knowledge there is no evidence that radiation has ever been associated with ball lightning. And other explanations beyond purely electromagnetic events to explain ball lightning have been suggested. Some include rare conditions involving things like phosphine or methane gas. Edit: Actually, that's not true. There was one scientist who claimed he found evidence of microwave radiation exposure, in wheat that was damaged from some kind of atmospheric event like ball lightning.
Yes, I realize this is a lot to digest and try to understand. Let me just try to put it simply: a gush of this gas coming out of the ground and reacting with air would behave very differently from a normal fire. The effects would seem to be completely bizarre, they wouldn't be anything like a normal fire. As for only one side of the body being affected, you can see these same types of effects from people in Iraq who suffered from white phosphorous fired by U.S. forces.
