"우리들이 개미를 먹습니까?"
Translation:Do we eat ants?
우리는 is also okay , when they generlize the thing they use 는 if they are talking about some particular people 우리가 can be used. Here they are talking about we all so 우리들이. Because its not fact thats why they didn't use 우리는
They actually are, you wait for the right season to catch the queens (they are big, more than a bean or two) and their abdomen is full of a fatty substance. Plus lots of protein, like any other insect.
Yes. Look at the Tips and Notes from "Verbs 1", which talks about 니다, and look at the Tips and Notes from "Formal Md" in the Interrogative section, which talks about "니까".