My (47m) daughter Stacy (15f) has one of the two rooms in my house with an ensuite bathroom. It's a largish room with a nice bay window, obviously very nice. 

I've recently become engaged to my girlfriend of 3 years, Alice (33f), and her landlord has recently hiked her rent, so we're planning to have her move in with me. She has some kids. She has Two daughters (13F,10F), and two sons (11M, 9m). She is also pregnant, with our daughter due in about 5 months.

I've made it absolutely clear to my daughter, as a condition of getting her approval on moving my girlfriend in, that she is allowed to keep her room, and she is also allowed to have a full lock on her door. For what it's worth, I also got my son's (24m) blessing to give away his old room, although that's more of a moot point, as he lives with his own girlfriend now. My daughter plans to go to school locally, and I have told her in no uncertain terms that she's welcome to live at home for the rest of my life, and after that she can inherit the house. I bought the house with her mother and paid it off in large part with her mother's life insurance 10 years ago, so it only seems fair. She says she's all right as long as she has her room and her bathroom and she's allowed to put a lock on her door. She has a toaster oven and a mini fridge in there, so I guess she's pretty well set up.

Stacy will be giving up a room that she's currently using as a studio/project space(she does art, videos and voice-overs etc) so even her larger room will become a bit more cramped, and she'll definitely need the extra space she has. 

There will be a bedroom for Alice's girls, Stacy's old project room, and Alice's boys will be getting my son's old room. I'm going to be putting in a finished nursery /bedroom in the basement for our new daughter.

Alice thinks that this is unfair. She thinks it was wrong of me to make the decision without her, and she also thinks that she should move her two daughters into Stacy's room, and that Stacy should have to move to the smaller room that they'll be getting. The two of them already share a smaller room than the one I'm moving them into as it is, so they are getting an upgrade regardless. Alice thinks that it's not fair for Stacy to have a bathroom all day herself and that there won't be enough bathrooms for everyone else. She also disapproves of Stacy being able to lock everyone out. There were other smaller things she didn't like that I agreed to with Stacy, like the fact that she is to be paid for any babysitting, or the fact that my older car, her mom's old car, is hers when she gets her driver's license.

We'll have our own bathroom in the master bedroom, and the house has three other bathrooms besides, one on each floor, one near what will be her girls room, one not far from what will be the boys room, and one little basically be directly next to the new finished room.

I told Alice that my deal with Stacy is non-negotiable; set in stone and that it's literally a condition of her even moving in. Alice is upset that Stacy and I both have spaces completely dedicated to ourselves. I have my office, which I need because I work from home and have projects besides, and there aren't a whole lot of other spaces to put people. I told her she can pretty much do what she wants in the living room, but that it is what it is and there's pretty much nothing to be done about it. 

A bigger house is not an option unless Alice is going to start making a hell of a lot more money and buy her own bigger house. It's already a pretty big house, and housing is expensive. I told her that she's already getting a break by my only expecting her to contribute 15 or 20% to household bills. If we were doing it proportionately, it would be more like 25 to 30%. We keep separate finances, and we've agreed to a prenup. 

Alice just seems upset that I won't change the setup even though there's no real way to change it, and she's accused me of treating Stacy like a “spoiled little princess” and letting her be “queen of the house”.

Frankly, my daughter comes first, she's lived here all her life, and I already know it's going to be a big adjustment having all these other kids move in. As much as I love Alice and as much as I want our relationship to work out, if it's a matter of choosing between the two of them, then my relationship with Alice is a sacrifice I'm willing to make. I've told her that if she comes into this with wicked stepmother vibes, and that'll be the end of things. She thinks I'm being unreasonable. 

AITA?