Otocinclus aren't the bravest of fish. They can be quite shy, but as they get used to the tank, they seem to come out more often. (my otos even swim with my speedy Danios!) There could be something that's scaring them, or the water conditions might not be quite right. Almost all Otocinclus are wild-caught, and are extremely stressed in the process. It doesn't help that the catchers use a chemical (cyanide) to slow down and hinder the fish for easier catching. This, along with often inadequate diet at the pet store, contributes to the Otocinclus' stress and shyness. Make sure your tank water is right, too:
pH : 6 - 7.5
Temperature : 70°F - 78°F (21°C - 26°C)
Water Hardness : 6° to 15° dH
If the Betta isn't bothering them, it's unlikely the Neons are. Neon Tetras are quite peaceful...
The otos are most likely hiding in the coconut because either it's hidden from other fish, or there's microorganisms growing in the shell.
Four otos in a 10 gallon is quite a bit...
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) and he hides inside the same plant all day and only comes out at night. My previous Oto would always be out during the day and the ones I see in stores are too, but I just figured Kitten was a rare exception. 
