"Well, Emily, this has been a very interesting day." Jeff says, feeling his sister chair's cunt tighten so much as it rapes his dick. "But why not make this more fun? I could ask you some changes I think of, and if you like them, I could write them into the book for us." He offers, as Emily moves him closer toward it. "Why didn't you say so before? I have no qualms if it makes this even sexier." She replies.
"What about giving you bigger lips? I'm sure you love kissing." Jeff asked. Emily squealed with delight, and let him write into the book. After completing the sentences under his sister's close observation, Emily found her lips growing three times in size. "Unf, feelth gudth" She said, a little muffled thanks to her plumper lips. Much like her pussy, she was able to extend her lips around and to Jeff's mouth, where she locked lips and invaded his mouth with her tongue. The lewd french kiss made Jeff even more hard, and thanks to the assault on his prostate and dick, he finally came into his chair sister's pussy.
"Ah, justht the firth batchth ob many." She whispered into his ear, before locking lips again. Feeling her brother's warmth fill her up, Emily kept massaging his nuts, to encourage even more precious cum production. "What else would she like?" He thought, making sure it was loud enough for her to hear. "Should we become married?"
Emily heard this and immediately came; "Oh god, yes! Please write that; I want us to be even closer together!" she stated. Jeff nodded and wrote down into the book that they were now husband and wife. But, what Emily didn't realize is that this came with the possibility that Jeff could divorce her. By wanting to be separated from her legally, someone else would have to separate them physically too. This could be his way out, just needed to bide his time.
With the change written down, Jeff and Emily had wedding bands appear on their ring fingers. Squealing in glee, Emily gets back to making out with her stepbrother-husband, milking him for more cum down below. Jeff merely needed to wait until he had the chance to tell someone that he was ready to divorce his stepsister-chair wife. Until then, he figured he might as well enjoy the pleasure; surely it couldn't hurt.