Cautiously...

You feel more fluid flow out around your cock head as she heard you offer to knock her up. Her body stops moving beneath you for awhile as she gathers her bearings.

"You would... want to get me pregnant?"

You nod enthusiastically and then work over her breasts some more.

A shiver runs down her body and she grabs you and starts to pull you towards her, forcing your member to slide deeper into her hungry quim. She nods at you and wraps her legs around your hips locking her ankles behind you to keep you from pulling away. Your rod swells even more inside of her as your mutual arousal increases.

"Oh gawd..." she moans, "I've never been fucked so good. Please don't stop. Give me your cum brother... make me have your baby. I want to feel it inside me growing... my tits swelling full of milk for you to share... yes... hurry..."

Your hips grind together over and over as you use her tight little box to bring yourself off. The tempo increases as your balls tighten up preparing to release your load inside of her. The head of your cock bumps her cervix and says hello. It drools all over the mouth of her womb like lovers in a particularly sloppy kiss delivering your amazingly thick pre-cum with the scout **** of your little soldiers. They fly into the breach as her womb decends to make their job easier. Swimming frantically inside her searching desperately for her waiting ovum. When the main **** finally arrives six waves strong, they find two already conquered golden orbs that the scouts beat them to.

Your sister passes out from extacy beneath you. You grab her pillow and prop it under her hips to help your boys along.