Not sure what you are seeing. A picture would be helpful. If the air sac is too big you can try to increase the humidity by adding a sponge with water in it.
From your description it sounds like the eggs are developing. Pictures would help.
Do the pics look anything like the eggs being candled here?
https://www.backyardchickens.com/t/261876/chicks-are-here-egg-candling-pics-progression-though-incubation