I think the idea is that when in a cursed sleep that you are still aware of what is going on around you. Snow knew she was in a glass coffin and Henry heard Emma say she loved him because he said i love you too. So when Jefferson talks in the hospital about collecting on the deal and Regina says that Emma was supposed to eat the apple so their deal is off, that Henry heard that. Though it is possible that something happens to fix that relationship a bit in Ep 2, so that Jefferson having a conversation with Henry won’t seem so bizarre.
Oh if they are going to do time travel then they cannot change the past, they can only actualize the future. If they go into the past, then they always went into the past and what they do there always happened. That is the only way they should do time travel. Or realm jumping, time travel.