Yes

After hearing his plea your sister just giggles to herself before replying,

"Oh baby no, your not gonna leave this room with anything functional down there. And even if I did pity you, which I don't, it's so much fun to pop them I think I'd just do it anyway! And chances are I'm gonna pop my bro's last one as well, it just feels too good not to!"

You swear you saw her glance over the the closet your hiding in but convince yourself it was just you imagination.

With that your sister gets down on her knees, opens her mouth and sucks her boyfriends last nut into it.

Due to the amount of **** already taken, the swollen orb fills her mouth and you actually think she looks pretty cute with her cheeks puffed up filled with nutmeat.

Slowly she begins to chew, always being careful not to break skin, and the ball slowly begins to lose its shape.

Over the course of about five minutes, the nut is thoroughly turned into mush. There is never a pop or any noise like it, just a gradual grinding into paste.

Finally she spits out the sack, now filled with nothing more than a liquid, which is when you cum.

You had tried to hold it in, but failed. You can only hope she hadn't heard or seen it...