When asked to refer to two or three poems in a question, how should we structure the essay?

You should firstly make a plan concerning the detailed points you want to present for each poem. Do any of them present the same point? If so, they can be linked together and put into one paragraph. Your essay should have around four or five paragraphs, in addition to an introduction and a conclusion. I would suggest demonstrating a main point per paragraph, focusing on one poem, with three quoted examples. You may be able to reference another poem, suggesting similarities and perhaps inferring contextual similarities such as the time period or the author. Other than this, it would be useful to focus on detail rather than sweeping statements used to pile in as many quotes as you can.