Natural

[Bichir Bro]

I heard you should overstock with cichlids to defuse aggression.

"Overstocking" is used almost exclusively for Mbuna, maybe Victorians too but im not very well versed in them.
Mixing fish, such as the ones you have, isnt a proper implication of that technique as youre mixing several different types of fish. Now while im not one to go into the whole South American cichlids shouldnt ever be mixed with African argument, youre more than likely to be faced with issues such as incompatibility down the road.

For the outgrowing, I know I will have to upgrade. I want to get a 125 gal minimum. But for the mixing, they've been together for awhile.

Assuming your parrots and dempseys are still relatively young, youre probably going to have some serious aggression issues once they grow. I doubt the two Africans will make it in there long term.
Especially if the "Iridescent shark" is the one im thinking of. Theyre ridiculously big fish when full grown and that combined with two full grown common plecs, two jacks and two parrots, a 125 with heavy filtration will still be heart pressed to keep up with that load.