Well. IMO you are not really overstocked but its more of a personal thingie

. Betta is not a community fish.. not because it is dangerous but because it can be a victem to fin nipping and most tetras are great fin nippers... They should mention with black widows that they should not be kept with long finned fish like Betta or Veil finned angels etc. Apart from this, they are indeed community fish.
Even as per the book rules, you can have 10" of fish in the tank but only if you have 1" fish. Sword tails are a tad bigger but tetras are kind of ok.
What is the filter on the tank? Any Live plants?
Nim