Jeff's first thought was to make his mother Stephanie's panties, to match the bra that was technically him. However, while controlling her, Jeff found that a little creepy. Rather, he decided to make her Steph's trousers, tight, but to be worn over what she was wearing already - a teeny bit less creepy, but he had after all been raised by the woman who'd found it acceptable to turn her son into her daughter's bra.
He walked Stephanie over to the machine, a teeny bit concerned by how naturally it came to him. He briefly wondered whether whatever it was that was giving him control over her body would also make it difficult for him to leave this form, but pushed the thought from his no-longer-extant head. He managed, using the home network, to find some photos of his mother, and used them to prime the machine.
He stripped her of the skirt she had been wearing, and spread his sister's legs in a very mannish way, ready to receive their mother. In a few moments, she would be wrapped around her daughter's legs, controlled by her son...