Oh I've done -tons- of research and I've gotten -tons- of help from firemouth breeders. They breed about 5 times a year. If they are too young, they can sometimes eat their fry, but that's okay, because they are learning

You can save some by "stripping the fry" (use a turkey baster and suck them out and put them in a clean 5 gallon filtered aquarium and feed them finely crushed flakes or baby brine shrimp). I think if they dug a hole again, they might be preparing to breed again.
There are tons of great resources - and even though this one is for angelfish, it gives you a great idea of the breeding process - I found it on youtube:
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part 1 of 2
and it's -extremely- helpful for egg layers in general. These guys share some attributes of breeding that firemouths do. The parents are very protective of the fry, they breed on similar surfaces, a flat stone or inside a flower pot. He goes into how to set up a tank for the fry, and he has a video of how to hatch brine shrimp eggs.
Oh and I wanted to add a video of my firemouth juveniles

Not to do with breeding, but this is the group I have. I took it on my iPhone, so it's not great quality, but you can see some of those beautiful specks of blue beginning to show up!
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Oh and experts, if I missed a point or said something inaccurate, please correct me

I don't have first hand experience, just researching.