What's the difference between 都 and 对?
I've been learning Chinese for 12 years and I don't think I've seen 对 used in that way before. However, the「对不是」 could be a typo of 「绝对不是」 "certainly not". So, maybe it could be this:


  我们都不是美国人。
  None of us are American.
  
  我们绝对不是美国人。
  We're definitely not American.


Hope that helps.