Them be my potatos, they do
why is it not 'As batatas sao as minhas' its possessive right?
You must drop the second article. So, word by word: The/As potatoes/batatas are/são mine/minhas.
So is it a mistake to use the second article in this context?
Maybe my reply to your other query would help here too: https://www.duolingo.com/comment/555355
Minha is feminine? What'bout masculine?
minhas = my/mine (feminine plural) ; meus = my/mine (masculine plural). 'batatas' is feminine, hence 'minhas batatas'
Why is são and not é? Is são plural?
Yes, são is plural
'Just one question. "Estamos" means "are" as per Google Translate. Could I have written "estamos" instead of sao(~) or not? Why/Why not?
Use "ser" with possessive adjectives/pronouns.