Duck eggs won't hatch?

Hello! I'm new to artificial incubation and have placed 6 fertilized dwarf duck eggs in the incubator. 3 eggs haven't hatched yet, so I've sorted them out. I'm on day 32 now, normal is 28 I think. Since day 30, one egg has been pecked, but nothing else has happened to the other two. On days 29 and 30 I could hear the chicks peeping, but now I can't hear anything at all. I really don't know what to do, should I help them out of their egg, or is it already too late, or will they perhaps hatch on their own? Thank you in advance for your answers.

LG