The only way you can really be safe is to learn at least 5, Durcan is a safe bet because it is the first year that he is on, and Yeats for obvious reasons, but you´d be better off learning off 2 more even just slightly just in case
I'm going to learn Durcan, Ni Chuilleanain, Yeats and Dickinson.
Durcan = first year, Irish (he does also have a connection to 1916)
Ni chuilleanain = woman and an Irish poet - usually one of each on the paper
Yeats = Irish poet, 1916, and he died. I wouldn't be sure if he'll come up or if they'll do the same thing they did with Heaney
Dickinson = I like her poems more than the ones left and they usually ask about her language and style.
My teacher doesn't recommend Plath because she has come up so many times in recent years, but I love her so I might give it a read over also.