Bothrops is a large genus of Central and South American Lance-Headed Vipers. They are crotalid snakes and range from the small Palm Vipers (formerly Bothrops now Bothriechis) and Eyelash Vipers Bothrops schlegelli to the very large Terciopelo Bothrops asper.
The three that you are asking about:
B. alternatus is the Urutu
B. atrox is the common Lancehead , sometimes called Barba Amarilla , or Fer-de-lance.
B. lanceolatus this one was originally the Fer-de-lance, now diminished in numbers in the wild.
So..they are three different species.
This is, however, a better discussion for the venomous forums..