Makes you wait.

She went out. She went out dressed like that. Well, legally she is covered, since her cock isn't real. You drag the coffee table back to the couch and sit and examine your doll and Amy's.
"Two fine looking ladies," you say to yourself. You hold one up in each hand examining them and comparing them. "I hold two sexy ladies right in the palm of my hand, just wish they were real."
"Oh, you sure are," a sexy feminine voice says from right in front of you.
You see that instead of the dolls, two hardening cocks are in your hands, one red and the other blue. "What?"
"You are holding us in the palm of your hand, Master," the red one speaks in a soothing tone.
You look up at their bare breasts, then down at their erect penises in your hands. "What?"
"I think he expected a puff of smoke," the red one tells the blue one. She closes your hand around her member so you don't let go, then sits beside you. "We just appear in front of you when you awaken us, master. So your hand was right where my cock appeared, so you got it in your hand. I would not mind you holding out your hand for my rod every time."
"My master isn't here," the blue one says.
"She went to buy some new clothes for me and her. Our butts are swollen."
"Wait, this..." the red one seems alarmed as she touches your bulge. "It has happened to mine, and I bet yours too," she tells the other demoness.
"Yea this invisible ****-"
"Impregnated you," Red finishes.
"-Came in me...oh," you end.
"You are already growing breasts, it cannot be undone," she feels your puffy nipples. "I'm sorry Master. The device we came from attracts predators that prey on legitimate customers like yourself. We can bind the predator to your service after it is born, otherwise it might kill you. We can't stop the pregnancy without killing you, however. You will have to birth it."
"Will it be another shemale?"
"Probably, bet you wouldn't mind that," Blue notes her hard cock in your hand.
"Be nice...even if he is under the calming spell. You won't mind the changes that are coming to your body," Red tells you. "Breasts, booty, hips, legs; you will be more like us than yourself from the neck down. Not many live afterwards, for various reasons, but I will make sure you do." She pats your left butt cheek.
"Thanks Red."
"Red? Oh- nevermind that will do. And she is Blue, then?" You nod.
"Creative," Blue yawns. She sits on the other side of you. "Nice thong." She puts her hand on your right cheek.
"Amy let me wear it. My butt is too big for my old underwear anyways."
"We can knock you up too," Blue tells you. "Since you will already have the milky breasts."
"Usually we wouldn't mention that, Master," Red tells you, glaring at Blue, "but you should know, since you will likely enjoy this pregnancy so much you will want to do it again. You just have to ask, OK?"
"OK, thanks Red."
"You're welcome, Master."
"Nice butt massage," you compliment them kneading your butt cheeks.
"Why don't you suck my cock for me?" Red suggests.
You nod, since it has been dripping for some time. You lean forward a bit and lick the tip, then work your way around the massive head. Meanwhile, you feel a tickling at your butt. The two hands pull your cheeks apart, and two squirmy pointed things crawl behind your thong and into your butt. They start pointed anyways, but their tails do get quite thick near their butts. You wonder how far they will go when they sit right up next to you, their bodies pressed to yours.
"Master, are you ready for a tail fuck?"
"A what?"
"Let us guide you, Master," Red reassures you. She quickly has you on all fours on one end of the couch, while the two demonesses turn away from you. They back up and their tails keep entering you until one cheek from each of their butts presses against yours. Then they just alternate pulling back and ramming their asses back into yours with a loud slap.
"That's quite a sight," you announce as you look back.
"I'm glad you like it, Master. I take great pride in my large bubble butt. Blue has a much larger one, but I think mine is more shapely and inviting."
"Everything on her is massive," you agree.
"You will be closer to her size than mine, in the end, Master," Red admits.
"Wow, really?"
"Demons aren't born as babies, that's not how it works. They are born as fully grown adults, hence the deadly issues. Imagine birthing me with my curves," Blue explains.
"Ah, now I understand that part." You don't feel worried. "So how would I birth a fully grown, fully curvy demon like Blue, and get through it alive?"
"Well, first we will sedate her, so she doesn't get to just burst out of you. During the pregnancy, we will work your ass looser than you could have imagined; loose enough for Blue's girth to fit in you easily, for example. Finally, we will enchant your breastmilk to finalize her bondage to you."
"What about Amy? She probably has two," you tell them.
"Well, she will be twice as large as you, then, at least in the belly. And we will need to enchant her breastmilk and her cum, since her second will be suckling there," Red responds, all while maintaining her pace.
"Ah, so I get hooters and she gets a dick," you state.
"Yes, that's right, Master. A female doubly impregnated will grow a cock in order to have two locations for the newborns to suckle. And it will be a big one, not like you will mind, master!"
"She can help stretch me," you look on the bright side.
"That's a good way to think of it!"
"Your tail is bigger, isn't it? I can't see."
"Yes Master, it grows with my arousal. Us red-skinned demons work this way, but only with those to whom we are bound."
"That's nice of you, Red," you praise her.
"It is not common to be aroused by our masters, you should feel proud," Blue tells you. "I hope my master is as good as you."
"Well, she's a blonde with a lust for cock and anal. Having a cock, that is."
"She sounds wonderful," Blue says dreamily.
"She will make a fine companion for you, Master," Red tells you. "Now then, Master. While I'm sure you are enjoying my tail growing within you, we do have a time limit. As our bond grows, we will be allowed to be fully-sized longer, but for now our time is almost over. This is for safety reasons."
You feel a sudden emptiness.
"Here is Blue." Red hands you the Blue doll. "We have a little time to ourselves, Master," she tells you as she moves directly behind you, matching you cheek-for-cheek.
"Oh, it really is growing, Red, it feels like it's completely filled even my stretched hole."
"Yes, it can get larger," she tells you as you notice it still swelling.
"I like this," you tell her. "It's like your butt is fucking my butt."
"That's what double-ended dildos are for, Master, though I will need to practice to take the girth you can. Oh, I'm going to cum!"
You feel hot liquid splash your feet. Then the her tail starts shrinking and she pulls it from you. She stands and walks to your face, her dripping cock aimed at your mouth.
"Would you mind, Master?" she asks thickly.
"Not at all, Red."
She moves to sit on the couch in front of you, making sure her ass rubs your face on the way down. You notice she has a pussy too.
"Where does your cum come from?"
"My balls are internal, unless you would like them hanging?"
"Sure would."
"Oh, I didn't think you would, since Amy will be growing a large pair. But as you wish, Master."
Her skin beneath her cock stretches outward in her lap, swelling to become round, then growing. They stop as they are about the size of cantelopes.
"They aren't even wrinkled," you note. You reach out to them and squeeze them. They are soft yet firm, and creamy smooth to the touch.
"I am glad you like them, master. You are making my tail grow again!"