You figured it would be safe and fun enough to just give Heather Rosalina's body. Having a little sister as powerful as Rosalina seemed... daunting, even if she'd have her personality keeping control of it. You drag the 'Body' option over, and Heather had assumed the name and appearance of Rosalina and vice versa. It would be strange to see Rosalina acting like your 5-year-old sister and taking care of the strange thing you made into your little brother, but you were starting to enjoy creating strangeness. "Confirm."
When time resumed, Heather - sorry, 'Rosalina' and Puppymonkeybaby were still watching TV, so you looked back to your phone. Looking at a wiki page for the Mario character now called 'Heather', things seemed about the same besides having the appearance and name your little sister had, though the TV shortly went to a commercial break.
"Puppymonkeybaby." Puppymonkeybaby seemed to get bored and then started walking off to the kitchen.
"What do you want to do now?" 'Rosalina' asked, following him, and so did Mickey - and you.
"Puppymonkeybaby." Puppymonkeybaby reached to open the fridge.
"I dunno if it's safe in there for you, li'l fella," Mickey said before picking up Puppymonkeybaby. Looking around, at the table was your father, busy working even at home, letting you briefly ponder who you could swap him with. "Why don't we take ya to your room?" Mickey said as he picked up the thing that was now his son.
"We can play there?" 'Rosalina' asked.
"Ya sure can, haha!" Mickey replied.
"Yay!"
"Puppymonkeybaby." You followed your three fictionalised family members to what used to be James' room. "Puppymonkeybaby." Upon being put down, your new little brother started going around and fiddling with toys, and 'Rosalina' joined in, giggling and playing around with Puppymonkeybaby. It was a truly bizarre scene, Rosalina acting so childish with one of the strangest commercial mascots ever conceived.
"Aww, aren't they precious?" Mickey asked, as the cherry on top of the weirdness.
"They sure are," you said. After a moment, though, Puppymonkeybaby went over to Mickey.
"Puppymonkeybaby." The strange thing started climbing on Mickey.
"Aww, I think he's hungry!" Mickey said, pulling on what used to be your mother's shirt and bra to free a breast. Was he really...?
"Is this gonna take a while?" 'Rosalina' asked, disappointed.
"You know Puppymonkeybaby takes a li'l while to eat, Rosalina," Mickey said, picking the thing in question up and towards his freed nipple. "You'll have to wait a little while!" Puppymonkeybaby started drinking from Mickey's breast, making you start to consider the fact you made this image right out of the depths of the internet's strangest corners a reality, and awkwardly started moving to leave, unsure how you felt about having witnessed that.
"I'll play with Stella," 'Rosalina' reasoned.
"Okay, see ya real soon!" Mickey said as 'Rosalina' followed you back out into the hall.
"Hi, Michael," you heard Rosalina say as you exited.
"Hi, Heath- ...Rosalina," you greeted her as she made her way down to Stella's room, where she was playing with her Barbie dolls.
"Hi, Rosalina!" Stella chirped as she entered. "Do you wanna play with me and Barbie?"
"Yeah!" you heard Rosalina (as you decided to just call her) reply as you peered in, wondering about swapping Stella. Swapping her with Barbie seemed obvious, but...
"Michael, do you wanna play too?" Stella asked.
"...I might just watch," you said with a smile as you entered the room.
"Okay," Stella said as you sat down. Stella seemed to have been playing with Barbie as a princess, and was about to continue with Rosalina until noticing you, and...
"Really, Michael?" Kevin asked from the hall. "You like watching little girls play Barbies? You weirdo!"
"Go away, Kevin!" Stella retorted. One of the few consistent things about Kevin was that he liked to tease Stella and the two could fight a lot, usually with intervention from your parents or another older sibling. Rosalina just looked worried, though, being only 5, though Kevin didn't come after her much.
"What, am I distracting Michael from your little tea party?" You tried to be a good older brother, but Kevin needed to be taught a lesson nobody seemed to really know how to teach him... until an idea popped into your head. "Come on, Michael, this is dumb and you know it!" You reached into your pocket with a smirk, and hit the button, stopping time.
"Not as dumb as you think," you said as time was stopped. Pulling the remote out, you selected Kevin, and then the Barbie doll Stella was holding. You'd swapped characters in pictures and videos with people - now for a toy with a human. This should inherently make for another unique swap, and would probably let Kevin see the other side of things... but what to swap? The first thing you thought of was to swap Kevin's body sans his face with the Barbie doll and maybe more experimentation with that 'social position' feature so that he would just be Stella's toy, which seemed like a fitting punishment even if he wouldn't know. On the other hand, though, you could leave him as a human and try to give him Barbie's femininity - he might not be one to tease Stella for being girly if he wore more pink princess dresses, you figured. That, and like you at that age, he might like a little 'reward' of being able to have his own female body to play around with if he's nice if you could figure out how to give him a human Barbie body. Maybe you could change the sizes, or an option to turn Kevin and Barbie's bodies into a doll and a human's body... but you might save that for if he behaves himself - again, not that he would know, but still.