For one, Jeff kind of felt left out, now that everyone besides himself is more or less female. However, instead of mimicking his sister, he had a different plan for himself. To begin, Jeff turns himself female. What shows on the screen afterwards is just essentially a female version of himself with almost nothing all that different actually. Just a bit of feminine features is all.
Jeff didn't mind it that much as everything would be changed soon enough anyways. To begin with, Jeff planned out everything and looked down at his notes just to be certain. The first thing he did was capitalize on two of his fetishes. Lactation and Egg laying.
He made the changes quickly, leaving himself with a pair of lactating HH cup breasts. Each of which, can produce around a gallon of milk every 12 or so hours, meaning he will need to be milked at least twice a day. Then, he gave himself a pussy capable of pushing out over a dozen, chicken egg sized eggs, also twice daily.
Now that those were taken care of, Jeff began sculpting out a better appearance for himself. It took some time, but he was more than satisfied by the beautiful young woman in the display looking back at him. Large breasts, cute face, sexy waist and a killer figure. But without much in terms of physical changes like the rest of his family now had, he still wasn't fully satisfied yet.
So he forked his tongue and lengthened it out enough to wrap around himself a few times over. He contemplated giving himself a snake's tail for legs, but decided against it and settled for giving his feet the ability to become any kind of footwear, or animal feet he wants. And whatever shape they are in, will not harm or cause him any kind of complications, such as muscle strain.
But that isn't all. Seeing as how his sister can now fly, and his parents can change up their physical shapes indefinitely, he still needed some kind of special, flashy ability. So after a quick brainstorm, he settled on two things, silk weaving and having semi-sentient, prehensile hair.
He first gave himself the ability to spin webs and create spider silk from his fingertips and even from his lower back if needed. Then he made his hair lengthen down by several feet, sprawling across the floor and all around himself. In the preview display, the girl's black hair clumped up near the edges and began moving around like testicles. They seemed to be serving her will, though he did set it so that they would act independently to protect him if he was in immediate danger. Finally, seeing as how all that hair would be annoying to always have around, he made it able to shrink down to falling just about down to ankle length. Though even in that form, his bangs could still move about freely.
Now Jeff was satisfied with everything and looked his profile over one last time, making sure it was all set up how he wanted it to be. With a grin on his face, Jeff changed his name to a more fitting female one, changed everyone else to remember him as such and sent his own changes through.