So does that mean Roland is really Zelena and Robin’s child?
I don’t think that’s what it means. I think Marian really existed. I think the Marian we saw in S2 episode Lacey was the real Marian. Remember how Marian was cursed while pregnant and Robin used the fairy wand to save her. Sadly, I think that she died soon after giving birth to Roland, since the fairy magic may have only been a temporary fix. I think Zelena simply then took her place by magically disguising herself as Marian and then hid amongst the villagers (unbeknownst to Robin) before she was taken prisoner by Regina’s guards, which was when time-traveling Emma saved her.