My daughter is 22 and
Sounds like you've got yourself quite the predicament. I think before you agree to let her back, you should definitely set some ground rules. I can understand how you would want them to be separated for the sake of your other children but you also have to understand that 22 years old is mature and adult. Would you treat an older couple any differently?
Ground rules- First make sure you have a deadline. If they move in in September - make the deadline something like March (to force them to be proactive and not just lazy). Second, demand that they find full-time jobs (I would also consider making them pay rent or utilities). The way I see it is that because your daughter is bringing home a boyfriend and staying in the house, theoretically they are renting a room from you.
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I have 3 adult kids and if it were me, I'd walk backwards on this one.
My daughter (25) moved back home in May while looking for a job and going to grad school.
Sorry, but I wouldn't recommend it.
My advice is to not let both of them move in, I wouldn't even let just her move back unless she was experiencing some extreme hardship. I let both of my kids move back home as adults, and it didn't go well with either one. They typically promise anything when they are trying to convince you, and then it goes downhill from there. That your dd is already arguing about the one rule you set does not bode well. After our kids have been living on their own for a while they often have a very hard time going back to the rules and housekeeping standards of a family home, especially one with younger kids. Even though my kids had lived with roommates they were pretty inconsiderate about a lot of things, and they did not do the chores that they had agreed to in the beginning. It leaves the parents to nag or be angry or both. Why invite more problems and stress into your house? With 3 teens you probably have enough!
Your daughter wants a BIG "favor" from you, yet is already balking that it's your house and your rules?
Back peddal, back peddal, back peddal on this one. Her balking about the "one" rule you've already laid down is a sign of things to come. Do not let either of them move in. What O Hearto said, they'll burn up your computer, eat your food, crank the air and heat, not clean, etc....
I wouldn't let them move in. That's a disaster waiting to happen. She already doesn't respect your house rules, so I don't think you'll get a lot of cooperation out of her. Just tell her you're sorry that you thought about it and don't think it's a good idea.
You're hearing from someone who's mom let his waste case brother move in. Yeah my brother was in his late 20's. His gf didn't move in, but she was at the house a lot. He didn't respect that we had school the next day and he would play loud music all hours of the night. He ate all the food. He broke my skateboard and didn't replace it (I'm still mad over that skateboard and it's been over 25 years).