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As for the species, this looks like a male A. hongsloi:
and this is a pair of A. panduro:
Your other male (post #9) is A. agassizii "Blue flame (aka Alamare Red tail)" and the female from post #5 can be some kind of agassizii female.
I'm not particularly good in sexing. But if fish 2 is in fact 4-4.5cm it's most likely a female. About the sex of fish 1 I can't say anything.
I'm not completely sure what you mean, but depending on mood a narrow pale stripe that separates the lateral band from the caudal spot can occur in A...
The strongly serrated dorsal fin of the largest fish, the caudal pattern and the orange/yellow color at the lower edge of the caudal fin. Moreover, the inverted coloration (bright lateral band and dark markings above and below shown by the specimen in pictures 3 & 4) I haven't seen in any A...
I don't know buit my guess is that males may reach 7cm.
Can very well be the case, especially for A. uaupesi and A. elizabethae: their type-localities are in the very same river merely a few hundred meters apart from each other. The type-locality of A. brevis is in a different river, but merely...
Here are some pictures:
https://www.aqualog.de/en/lexikon/apistogramma-brevis-4/
https://www.aquaportail.com/especies/ficha/pez/3482/apistogramma-brevis
https://fishbase.mnhn.fr/photos/ThumbnailsSummary.php?ID=46595
The two supposed fenales show a distinct gap between lateral band and caudal spot. I haven't seen this in any elizabethae so far. Imo they are likely a different species.
Among other things A. sp. Steel blue have a vertically extended caudal spot that is separate from the lateral band, these fish don't - they are 100% sure borellii.