why isn't it "מכינים" or "אופים"? It would technically be grammatically incorrect, both in English and in Hebrew.
I know that, but considering the fact that there is a verb (אופים/ofim/baking) that means to make a cake, muffins, etc., why would you use עושים/osim/making?
Maybe it is a cold cheesecake that goes in the freezer and doesn't get baked?
All of these verbs can describe the making of a cake. However, in this exercise you were asked to translate עושים, and the translation of the word עושים is making :)
It's not. It's a general statement.
Like "how does one make a big cake".
There are different ways of saying it.
I don't think "they" is used in English for the same purpose.
French uses "on" which is closer to they. Or we, perhaps.