It's your (of legal age) younger sister!

"Ignore it," Jan urges, her words somewhat garbled as she tries to speak with a mouthful of dick.

Feeling uneasy, you try to concentrate on the sensations. But the ringing is insistent.

"Whoever it is, they won't go away," you say.

Just then, the latch clicks and ice fills your veins as the front door swings open. Standing in the doorway is your other sister, April. You'd known she had a reputation for dropping in on friends unannounced, and now you get to experience it for yourself. Lucky you.

"Hey, I hope you don't mind if I... oh, wow, that's awkward," she says.

Your body tenses and your heart pounds. You try to stand up, but Jan pushes you back down. She pauses just long enough to give April a sideways glance, then resumes her oral work. If anything, the fellating becomes more vigorous and punctuated with exaggerated slurping sounds.

"Uh, no, no, it's fine. This isn't, um, what it looks like," you stammer.

April looks from you to Jan, then back again. "Are you sure? It kinda looks like our big sister is sucking her brother's dick."

"N-no, really!" you protest. "J-jan and I have an arrangement."

"Yes you do," April says with a laugh. "Holy shit!"

Surprisingly, this doesn't kill your erection. As you stare dumbly at April, you hit your climax, blasting a load of cum into Jan's mouth. Your sister swallows the spurting torrent, then sits back on her heels, wiping her lips.

Your younger sister shuts the door and comes over to sit on the other side of the couch. "Well, this is certainly a surprise," she says.

"No shit," Jan grumbles, still licking her lips. "What are you doing here?"

"Well, when you told me what you two were up to, I couldn't believe it," April explains. "So, I had to see for myself. I mean, who does this kind of thing?"

Jan sighs and rolls her eyes. "So, are you here to help or not?"

"Oh, absolutely," April agrees. "I'm down for a little incestuous fun."

I flinch, expecting Jan to lose her shit at mention of 'The I Word'. But she just looks annoyed and even a bit flustered.

"Don't even joke about that," Jan complains. "It's not..."

"Yeah, I know," April says, waving a hand. "It's not like that. You've got an arrangement. So, where do I fit in?"

"You don't," retorts Jan. "I never asked for help and you don't live hear."

"Yeah, about that. I'll be starting uni around here soon and I need a place to stay. Mom volunteered you. You've got room, right?"

"No."

"Great, I'll bring my stuff up."

April jumps up and hustles back out the door.

Jan glances at you. "What do you think?"

You blink. "Me? Uh, I'm not sure what to think, honestly."

Your head is still reeling. Your younger sister just walked in on you and Jan getting nasty, and now she wants in? You hadn't thought that April might go down on you too, but now that the possibility has been brought to your attention, it sounds pretty damn hot. But you're struggling to think of how to navigate the Jan-sized mine field to get there.