"If I'm going to experience life as a woman, I'd rather it not be as someone so...experienced. No offense, Mom, but I have a different suggestion. How about I switch with Emily, and Emily switches with you?"
"I think I could work with that. I'm more interested in being young than being a man anyway. What do you think, Emily? Do you think you could spend some time in my body?"
Your sister thought about it. She's currently been very uncertain about her future, and skipping some 20 years of her life and getting a job, a house, a well-maintained savings account and a family instantly seem very enticing to her.
"Sounds like a plan. You're sure this is safe, right?"
"I guess we'll have to find out!" you say, and quickly start cutting open your sister's skull before she can object. You remove the top of her head and cleanly remove her brain. It came out easier than you expected, which you chalk up to the magic of the rapier.
"Ah!" gasped your sister. "Whoa, I can still talk! I can see, too!" She felt the top of her head, and the empty hole where her brain used to be. "This is freaky..."
So far so good. You place her brain and skull cap on the table by the bed, and hand the rapier to your sister. "It's as easy as it looked. Just cut open my head and take my brain out, and then put my brain in your head."
Your sister smoothly slices your head open and removes your brain. She turns it around and carefully places it inside her head, and suddenly your body falls onto the bed like a doll as your brain connects with her body instead. Your perception suddenly shifts into her body. You look down and pass your hands over your new, feminine body. Your sister clearly inherited your mother's good looks, and you get a good feel of your/her well-shaped and sizable breasts. You suddenly realize what happened to your body, and figure that your sister must be trapped inside her mind at the moment.
"Crap, we gotta get you and Emily's brains swapped, she must be scared to death!" You grab the rapier and quickly remove your mother's brain and put it in your body. Your mother's body falls limply onto the floor, and the two of you quickly pick the body up and get your sister's brain into it.
"Ah!" screamed your sister with your mother's voice. "I couldn't see, hear, or feel anything! How long was I gone?"
"Only a few minutes." said your mother with your own voice. You can already tell it's going to take a bit to get used to these voices.
"It felt like half an hour. Let's make sure not to do that again." Your sister felt the top of her head. You notice she's missing the top of her head, and you realize that none of you have complete craniums at the moment. You all sort out your skulls and make sure your brains are firmly secured inside your heads.
Your mother looks down at her new, masculine body. She grabs her/your crotch and you notice a slight bulge in her pants. You blush, and your sister notices your staring. She looks over at your mother and gasps slightly. "It looks like this is getting fun already." says your mother, feeling her erection. "I never knew how big you were, John."
You cough awkwardly. "Well, I'm big in quite a different area now."
"Aw, I don't get any new bits to play with." says your sister, frowning slightly.
"Perhaps we can change that..." says your mother, mysteriously.