You hit upon a pretty good idea, but you also think about how you want this to play out. Sure, you could just give everyone their commands and be done with it, but you've been doing that all day. Besides, Dan should be the one to discipline his daughter... even if you are the one putting the words into his mouth.
"I'll talk to her about it tonight after dinner," Lindsey said, not realizing what you had in mind, "It'll be better coming from me, and I can make sure she knows we're not-"
You suddenly speak up in your 'command voice', ~You will both disregard your current plan, and your current opinion on Emily's masturbation habit. You are both instead rather angry about it, and wish to begin her punishment as soon as possible. And you both agree that this is the best way to do it...~
~~~
A few minutes later, after you made sure that both Dan and Lindsey understood their commands, you go upstairs and knock on Emily's door, "Emily, it's Eric. Your parents want to talk to you."
Emily opens her door, "Alright, I'm coming. Is it serious?"
"Sounds like it," you reply.
She sighs, "Great, wonder what Dad's worried about now..."
You let her go ahead so she doesn't see you smirk. Making your way into the kitchen, you and Emily are greeted by the sight of her parents, looking very angry at their daughter.
"What's going on?" Emily asks, suddenly looking uneasy.
"Emily," her mother says sternly, "Were you masturbating in your room earlier?"
~Answer honestly,~ you command Emily. You're thankful now that you thought to include a 'you cannot hear me command others' clause while you were telling them how this would go down. Just to be safe in the future (and save yourself the trouble later), you add, ~Oh, and from now on you will not be able to hear commands I give other people that don't affect you.~
"...Yes," Emily mutters, her face going red, "How did you know?"
"I spied on you without you knowing while you were doing it. You're into some interesting stuff," you said, adding ~You will not find what I did inappropriate or offensive.~
"What the hell, Eric?" Emily yelled, and for a moment you thought that she somehow didn't hear you, or worse managed to resist the command, until she continued with, "How could you tell them I did that? They're my parents!"
You breathe out a small sigh of relief. Well, that was an unexpected yet amusing gap in your order. She may be fine with you knowing about her habits, but she still doesn't want her parents finding out about it.
"Which is why he was right to tell us about this!" Dan snaps, "You're too young to be looking at that kind of smut, or touching yourself like that!"
"No I'm not!" Emily shouts back, "I'm fourteen, and I already know all about what sex is! Mom, tell him!"
"Sorry sweetie, but I agree with your father," Lindsey says with a frown, "Just because you know about sex doesn't mean you're ready to have it, even by yourself. You've still got a lot of growing up to do."
"Oh, come on!" Emily groans, "It's not like I was doing drugs or actually having sex! I don't see what the big deal is."
"Exactly!" Dan says, "Which is why your mother and I have decided to punish you so that you'll understand just how big of a deal this is. From now on, you have lost the privilege of managing your own body."
Emily's eyes go wide in shock. It takes a few seconds for her to process what her dad just said, but when she does she screams, "...WHAT?!? What does that even mean?"
Dan glares and Emily, and says, "It means that from this point forward I forbid you from touching any part of your body that you might otherwise 'play' with, directly or otherwise! That includes your butt, your chest, and your... 'lady parts'."
You chortle a bit at this euphemism. Not exactly what you told him, but even when mad Dan is clearly not comfortable talking about his daughter's vagina.
"That's insane!" Emily protests, "What, you expect me to not wipe myself after I take a piss?"
"Exactly," Dan replies, "You have clearly proven yourself to not even be trusted with something as simple as that!"
"Well then how the hell am I supposed to stay clean?" Emily asks, "Unless I'm supposed to walk around with crap in my pants all the time."
"Of course not," Lindsey says, "Eric will help you with that from now on."
For the second time in five minutes, Emily's mind is blown. She looks over at you and shouts, "What?!? Him?!?"
"Yup," you say with a smirk, "You could say I'm your new 'body manager'."
"This is messed up!" Emily says, turning back to her parents, "I'm not letting him do that for me!"
"Oh yes you will," her father scolds, "In fact, you'll let him do a lot more than that. Eric is going to supervise you when you bathe, or go to the bathroom, or anything hygienic like that. Furthermore, you are not allowed to wear anything, and I mean ANYTHING, without approval from him. No clothing, no make-up, no underwear... in fact, just to be safe, he will be the one who puts your panties and bra on, just to avoid any temptation on your end. Basically, in terms of what happens with your privates or your appearance, what he says goes. He has full permission from us to do what he sees fit to make sure you learn your lesson."
"But we just met him!" Emily shouts, "This is crazy! Messed up! Mom, you can't be okay with this!"
"I'm sorry, Emily," Lindsey says sadly, "I know this seems drastic, but you have to learn somehow. And we trust Eric with this."
And they will no matter what, you think to yourself, remembering that part particularly well.
Emily shakes her head and starts backing away, "Nuh-uh, no way! This isn't right! I'm not going to let you do this!"
"You will if you don't want to be punished even worse!" Dan snapped.
"What is wrong with you?!?" Emily shouts, starting to look frightened.
"We just want what's best for you, sweetie," Lindsey says soothingly.
Realizing that you should probably intervene before this spirals completely out of control, you command Emily, ~You will not find anything deeply wrong or inappropriate with this punishment, nor anything that has been proposed by your parents or myself. You don't have to be happy about this arrangement, but you will agree to follow these new rules, if only to avoid further punishment by your father, which you will also find reasonable if it comes up.~
Emily stops backing towards the door, though she still looks incredibly uneasy. The room is silent for several seconds, then Emily asks, "How... How long is this going to last?"
"However long it takes for us to believe you've learned your lesson," Dan said, finally calming down somewhat. Of course, your command was for it to actually last as long as you want it to, but as far as Dan and Lindsey were concerned, your word would be the only thing that would convince them that Emily had 'reformed'.
"Until then, I'll be staying here with you guys 24/7," you say. Thankfully, you don't live with anyone who would question you disappearing for a while, as long as you kept paying rent.
"...Don't you have a job or something you need to go to though?" Emily asks.
"From now on, this is my full-time job," you reply, somewhat truthfully. Sure, you had a real job, but given how powerful this sapphire was turning out to be, you probably don't need it anymore anyway.
Emily sighs in resignation at her new situation, then turned to her parents and asks, "Is that everything?"
"As long as you understand what the rules are from now on, we're done here," her father said, "You can go back to your room now if you want. WITH Eric."
"Yeah, yeah, I know..." Emily grumbled, turning on her heel to leave.
"That girl sometimes," Lindsey mutters to herself, then said to you, "I'll be sure to make some extra food for dinner, since you're sticking around. And Emily can help you find spare blankets and such if you need them."
"Thanks, Lindsey," you say with a smile before following Emily upstairs. This new 'job' was going to be fun.