Well it looks like they did develop but even if your incubation parameters are perfect then you may still have one egg that doesn't internally pip and dies from something. I have had 100% hatch from viable eggs but I have had 50% too from my own doings, in hindsight.
Did the others hatch on day 21 or 22? If they did then I would assume the 2 eggs left are dead. I would take the eggs and slowly crack the egg at the top of the air sac and inspect as I went along to see if it moves or chirps. When you get the shell gone where the air sac is, you will know more by looking at the embryo whether it is alive or dead.