Vincent,
I would suggest that you skip the pygmy corydoras. If you need some dither fishes, try pencilfishes instead.
As for mixing dwarf cichlids, if your aquascape or tank layout has plenty of hiding space and there is no line of sight between the two pairs, you might have a chance that they will not clobber each other to death should one of the two pairs decide to spawn.
Cheers,
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