I've recently come up with a theory and I thought that others should tell me if they think it's legit or uh.. 'poop'. This theory revolves around Finding Nemo's first scene. As far as I'm concerned, I've seen no other participants make this theory. So let's start! Also, the other clown fish, I think, were only two or three fish because I think only two or three would think of doing something like this.
Notice when Marlin gloats about how many of the clown fish wanted to live in the Great Barrier Reef, in that exact 'house'?
Secretly, the other clown fish were sneaking around Marlin & Coral's home in order to make them move out so they could get it instead. I don't think that they were involved with making the eggs visible, that was Coral and Marlin's fault.
The first part of the plan was to get everyone in the 'neighborhood' (other than Marlin & Coral, obviously) to be out of harm's way so their motive would be successful with no one who wasn't involved to suffer. They did this by only telling the residents that a predator will be coming to that exact neighborhood very soon, therefore the reason why everyone else was safe.
Now, the predator is where it gets tricky. I think they either bargained with it by promising the lives of all the fish in the Great Barrier Reef but secretly, the other clown fish would only allow Marlin, Coral and the offspring to be in any real danger as they would be the only un-notified fish (#DoubleCrossed!) OR they tricked the predator into coming to that exact spot by maybe taunting it with an already dead fish (or any other food) but once being led to the two already living fish, decided on attempting to eat them instead. Sadly, only one lived.
The plan was to simply scare both Marlin and Coral out of living in the Great Barrier Reef by making them think it was not safe as they had the eggs to think about so the amazing home would be back up for sale. I think that while Marlin fell unconscious, they realized that the predator was going to hurt the children when they saw Coral eyeing the eggs instead of getting inside. And thus, the other clown fish attempted to save the eggs.
Though they were meant to be in danger, no one was meant to be hurt. Coral and the basically over-jealous clown fish only saved one of those over 400 eggs which got his own movie. Coral, the eggs and their own death's were caused BY A MISTAKE!
It might be a bit of a stretch but, it's fun to think about anyway.