For those wondering about size when they aren't incubating ....
May 4 (not long after incubation began)
June 3 (this morning)
Princess is in the top corner, Smiley on the bottom corner. (Photo on the left is slightly more zoomed in than the one of the right)
You can see there is a difference in body size but not as much as with Ivy. If you look closer, you can see that Princess has more mass than Smiley and her wings/tail are a bit longer.