@Rocky998
I am trying to sort out the timeline here, please correct where needed
You lost a fish the week before last sometime, around 12 days ago.. Said that you have two fish that seem to act out aggressively and you thought they were why the fish died.
Last Tuesday you posted that you had bought another one on impulse due to the threatened legislation to replace the one lost the week before.
You have since lost that one due to what you assumed was stress but in all likelihood it was attacked by the existing two and not seen the existing two since Thursday.
First of all....you REALLY need to slow right down and find out exactly the cause of the original fish death and its replacement's death.
I don't know...maybe
@itiwhetu can throw light on this.....but to me as someone who actually feels this species of fish are maybe a little beyond your ability (and I do not mean that in a nasty way but as in not everyone can handle the more complex and aggressive fish when still learning the art of fishkeeping). It sounds like the two aggressors "removed the weakest link" by force, ie bullied it to death. Quite possibly picking up a few war wounds along the way. Within days you replaced the dead fish with another of the same species, thus a "new" intruder to be dealt with. The two aggressors again "removed the weakest link" by force. And probably picked up yet more war wounds.
You could not find them, started ferreting about in the aquarium moving everything...and thus shifting their territory and disorientating them....which would stress them to the nines especially if eggs are involved. The stress of dealing with not one but two weaker fish/intruders in their back yard followed by you messing with their aquascape would be more than enough to kill fish.
I would have that spare aquarium up and running before you start taking the big one apart cos those two fish are probably going to be in a bad way when you find them.....if infact they have survived this experience at all.
If they have not emerged by tonight with the lights off.....they are either injured, deceased or just too terrified of this big human who keeps ferreting about in their home and are doing all they can to hide from you, even hiding in places that you would never dream of looking.