I had 4, 1 disapeared, 2 died on vacation, 1 just died like an hour ago. Parameters are fine, I do weekly water changes, and they seem to get plenty of algea.
Otos are difficult, if not impossible, to acclimate to a new tank. I had two out of nine survive. But once acclimated to your water source, then they can be transferred back and forth if you have multiple FW tanks. I put in extra StressCoat because they are sensitive to chlorine. Maybe you should age the water for a few days or even keep an empty tank of water with a filter running to use as a water source.
Another thing to consider is you should actually feed the Otos, sorry if you did but you shouldn't relay on the algae in the tank keeping them, see http/www.otocinclus.com/.
If you intend to keep the 10gal I would not add a bristlenose! 6inches is a lot of fish for a 10...