I googled and got this:

How can I tell a male oto from a female oto?
It is not that simple to tell the gender of an otocinclus, since the males and females have the same coloration. You need to wait until they're nearly adult size before the differences are noticed. As with corydoras, the otocinclus catfish females are usually larger and more plump around the midsection (when viewed at from above).

Is your oto slender (while still having a chubby belly) and more streamlined? It's probably a male. If on the other hand your oto is wider across the area behind the eye and in front of the dorsal fin, as well as being taller in this place, it is most likely a female. Another way to tell is from the underside instead of from above. If the belly is wider than the one of the oto next to it, it's most likely female.

Now if I can get mine to cooperate maybe I can tell what they are, I have 2.

 

See, mine boh have the same body shape, although Patches is smaller. They look like rounded rectangles with tails xD

 

Can you post pics of them from the top?

 

That's the two of them (lucky being the older).

I'm assuming patches is still growing but he has the same body shape as her.

 

The larger one is definitely female, but I ca't tell with the younger one.

 

I'm slightly afraid that if it is a male, they're going to breed.

But the water conditions aren't good for that, thankfully.

 

If they breed I will take ALL THE BABIES!:lol:

 

You don't have to worry about that- even when Otos breed the babies RARELY survive. It is almost unheard of for them to breed in captivity.

 

That's good xD

Very good lol