Three otos is too many. It's only a 5 gallon tank and with substrate et al, your actual water volume will be closer to 4 gallons. Otos like to be in groups of 3 or more but in a five gallon, I'd just go with 2.
It all depends on your betta. I had 2 otos in with mine and eventually found one half-eaten and the other cowering under the cave. I moved the other into my 55 but he was already hurt and died pretty quickly.