Very unfortunate loses. I don't have any insight.
However, I do believe you have 2 species in the surviving group: i) the "red tail Hemiodus" (almost certainly H. gracilis). These are most of the specimens in the videos. Then, ii) another species with two defining characters: incomplete black stripe from mid-body to tail, and no red on caudal fin (very white instead); the fish is also more robust (thick). I only see one specimen that I think belongs to that second species, but it is hard to tell. The two shots below come from the last video, at 3:42 and 4:06 respectively.
From your video (apologize for quality of clips, not of the video):
Several things make identification of Hemiodus very difficult: Generally, we don't know the localities they come from; also, there are a number (10-15) similar-looking species, all relatively poorly known, and some are sympatric (exist in the same locality); also, some of the defining characters (extend of black bands or spots, presence of red on caudal fin) are mood-dependent, developmental (age)-dependent, and potentially also affected by individual variation, and both gender-based, and dominance status variation.
I have what I believe are two species, together in a 125g-
- 3 large specimens (perhaps H. orthonops or similar), characterized by almost never complete black stripe (instead, just a large dot at mid-body and rest of body completely silver), and mainly no red on tail, white instead. However, as these specimens grew from 3.5-3" to now ~7-8" (I believe they are done growing), red appeared on part of the tail (both upper and lower lobes) in a permanent manner (both upper and lower body), albeit much less (size of colored area and intensity) than in H. gracilis. Also, in a mood dependent fashion, the single black dot mid-body can develop into a nearly complete black line (most often greyed-out as a 'ghost' stripe), which can change later or next day when mood changes, by intensifying or disappearing. These ghost dark bands are hard to catch in pictures. I have had these fish for about 5 years.
- The second species (2 fish, ~3") have a more permanent black stripe (although there is also a marked dot mid-body), and no red at all on fins, white/silver instead at the two edges of the lower caudal lobe. Of course I do not know how they will change with age, and also don't know how large they will become. I have had these fish for ~ 1.5 years (originally 4, I lost 2 to jumping and to my stupidity).
I don't intent to do piracy to your thread, rather to offer images of my fish for comparison and discussion.
The 3 large specimens first (two visible),
and just for kicks! (they are fast!)
Composition of one of the two smaller fish ('sp. 2').
Cheers and thanks for sharing.