Beginning to think my duck eggs failed

On March 3rd at our local livestock auctions, I purchased a batch of 12 fertilised Indian Runner Duck eggs.

15 days into incubating them in my Janoel, I candled the eggs to find 4 were complete fails and I had 8 viable eggs.

Duck eggs take 28 days to hatch according to all information sources.

My incubator has ticked over to Day 29 from the day I put the eggs into the incubator. TWO have started hatching, but in a 12 hour period, they've only successfully managed to make a hole big enough to push their beaks through... I first noticed that they were hatching at about 5am, its now 9:48pm and the progress hasn't been a lot. I don't know how normal or not normal this is, as I've never hatched ducklings before, only chickens. Am I supposed to HELP them or something??

Now, as for the other 6 eggs? I can't hear any peeping from them, no tapping, they're quiet as the grave in there... How much longer should I give them before I just cut my losses?

Well, the first 2 hatched.... but the other 6 I've still not heard a sound coming from them.

They're still quiet and nothing appears to be happening, a day later than it should have started.

My little bubs are out in their brooder. One of them is "sunning" itself under the light. LOL.

Still nothing on the egg front.... :'(

Hatchery isn't getting off to a very good start, our first ever batch of eggs and only 2 have hatched out of a dozen originally.

Not good.

Incubator has officially turned over to Day 30 and the other 6 eggs haven't even peeped. I think they're dead.
Can anybody tell me what I should be seeing if I were to candle them?