" all leg sections are worked at the same time using separate balls of yarn for each section"
You need to make two leg openings. You will work a section of the body which becomes one side of the underbody, cast off a few sts that will become one leg opening, work more sts for the back of the body, cast off a few more sts for the second leg, then work the remainder of the sts for the other side of the under body. These three sections need to be worked separate for a couple of inches, depending on which size you are making. Once the leg opening is the size needed, you join it all back together into one piece to complete the body. Good luck.