Improper humidity and temperature during incubation can cause some defects - I would post this separately in the forum to ask opinions of what to do as I’ve never had a chick hatch with any leg issues (though many people have). You might want to try and split it or correct it according to the advice of others on this forum as some of these issues can be fixed in a few days and that would be best for the chick.
I would also leave the other two eggs be, as even if the air cells are  too large, fiddling with them now isn’t going to help at all. If they don’t hatch, feel free to get photos of the air cells so we can see what you mean. I would suggest getting a hygrometer to add to the homemade incubator so you can keep track of both humidity and temperature - this will probably result in better hatches. Try to make sure the thermometer is down by the eggs as it usually is colder down there then the top of the incubator for still air set ups (and this could also partially be why the eggs are delayed).
Hello!!!! It's day 26 and still an egg hasn't hatched. If you don't remember, earlier I had mentioned that three of my eggs had a large air cell. One from that hatched successfully while the other pipped and died while inside the shell


It was really heart 

 to watch him die.
I have waited till this day(day 26) for my last egg to hatch but it still hasn't. I could see a fully developed chick inside while candling but I don't know if it is alive. As you had asked, I'm attaching the pictures that I took while candling.
One side has a large air cell but if turned to the other, it has large chick within. Please do tell me if it will hatch anymore. Shall I wait some more or break it to see what's inside?
You’ve done quite well with the hatch so far considering your set up and experience, so obviously you’re doing some things right. Ultimately if the eggs are fresh/clean and from a good source, it comes down to three things: humidity, temperature, and turning 
