I suggest dropping the Silver Dollars and reducing the number of Severums to 1male or 2 females.
 
Silver Dollars can be fairly skittish which doesnt go well in a tight tank
 
There really isnt enough space for the Severums to spread out and two adult males will likely not want to live on top of one another. If a pair forms the third will be in trouble. Also if a pair forms they will likely not share space with tank mates causing them to be overcrowded on the other side of the tank.