Dear god my houseplants have some kind of fungus 😦

1) how the eff do I get rid of them? Fungicide 3 + drying them out doesn't seem to work
2) is it harmful to have these in the house? i.e. am I breathing in nasty spores that'll infect / mutate / breed into a new strain of bacteria specific to humans 😦🤯
3) how do I keep them from spreading to other plants? why / how did new breeds of fungus develop in these plants??🤯🤯🤯

Unless you are very susceptible to spores and fungus you should not be effected at all.
These things are much more common when you use old potting soil or add outside garden soil. A good potting soil is sterilized to remove these things. As a fungus, they feed on dead and decaying matter, NOT a live plant.

Just as my opinion, you have been watching too many horror movies! There are not going to mutate spontaneously and kill humans.
But in the event you are kidding, relax, you'll be just fine.

I've had this problem too. I introduced mine because my kitty wanted to dig in my large potted plant. I covered the surface of the soil with some shale I found in the yard and suddenly, mushrooms! The spores may have come in the potting soil or drifted in through an open window or door.

The spores are everywhere but the mushrooms will only kill you if you eat them. Pull them up before the little "hats" open to keep new spores from being released into the soil. Sprinkle cinnamon on the surface of the soil. Keep pulling and sprinkling until no more show up.

Thank you, Daisyl! I'll certainly try your suggestions. Love the "hats" reference, btw. :)
Thanks, BigBill. The mushrooms are super creepy! Good point about horror movies.

I thoroughly enjoy eating mushrooms, although not the same type that you have! Not so creepy!

I hope you don't eat this one as it is poisonous.