I made two dresses for my two daughters in 1974. I had this beautiful fabric, and had to get two dresses out of it. I made the tops with knit (could be t-shirts), then cut the fabric in half so each girl got their share. When I sewed the cotton to the knit about waistline height, I stretched the knit as far as I could. After the seam was made, the knit relaxed, and the cotton looked like it was a little gathered. Plenty of room to put over the head. Those two girls wore their dresses a lot. They were not twins, but the younger one was tall for her age (she is 6' now) so they looked like twins. They called them their "dancer dresses".

I use to make them for my girls ...shirt over the hips then gathered skirt