Be nice if they turn out to be otos.....I'm just really on the fence about what I think they are. Some of the pics look like baby plecos....but sort of emaciated. Some look like otos. But there's no side stripe, no white belly. You have to post pics of the dark adult otos you have. Otos are extremely tiny when hatched, really really tiny...so if they are otos, they've been in ther quite a while. Throw a piece of zuchini in there. I just think whatever they are, they need more food.
Compare the your picture in post #10 to this, side by side have both pictures open on your screen
http://www.otocinclus.com/. The eyes aren't placed right for an oto, and there's the little what I call a whisker that curls up on the face of your pic #10 on the right side of the face...that's pleco.....take a look and what do you think?