Sharing a Nesting Box

I wonder if two of our nesting boxes are too big, uncomfortable or close to the door to our chickens liking. When our chickens first started laying, they mostly used nesting box #3, but still used #1 and 2 a good amount. Now they practically never use #1 or 2, we probably only find one egg there every two days. Sometimes we we find twochickens in the same nesting box (always #3). Some of our chickens don't fill up all the room in one nesting box, but I think it must be pretty squishy when they share. They must really not like the other nesting boxes if they share so often. One reason why they like nesting box #3 more than the others may be because it is the farthest away from the door so no cold air comes in, and it not too big. Nesting box #2 is a bit bigger than the other too, and #1 is right next to the door, so neither of them are good. I sure hope that sharing nesting boxes isn't bad!
P.S. fuzzy chicks in 14 days!