What are you willing to do to make her trust you?

Make a new rule

Contemplating here predicament and knowing that you really want to fuck her. You go back to the rule book for a moment.

New rule: when a set of twins is asked to do a sexual act to help the other one out, the requester must follow through with his end of the bargain or instantly be punished with jail time and have his gender changed automatically. For every point of IQ the twin that needs to cum has the lost the requester is changed for a day. Snapping the book closed you wait anxiously as the twin in white adjusts to the new rule. As it sinks she says "alright ill do it." Then carefully and sensually she crawls on all fours her ass pointing up to the world as she unzips your pants and your already throbbing fuckstick flops out. Gingerly she lifts it up and laps at the tip her velvety tongue sending slight waves of pleasure through you. Still going slow hoping not to get noticed you come up with an idea. While waiting for her to get to the good part you stealthily open up the rulebook once more Old rule: Sex in public is viewed as a beautiful thing and is not illegal and no one may interrupt a couple indulging in such an act until at least one party achieves orgasm.

Satisfied with your handiwork you wait a moment as the old rule takes effect. As you scan around you see you're not the only ones perfiming sexual acts. With the old rule in effect the gorgeous twin sets to work stroking your meat faster as she envelopes the tip in her soft lips and velvet tongue. Smiling as you feel accomplished with your new found abilities. You lean back in your chair as she pumps you into her. Unexpectedly she looks up at you lust in her eyes as she pulls back then dives all the way to the hilt impaling her throat with your 9 inch fuckstick. Letting out a surprisingly loud moan you watch as she works her magic feeling yourself getting close you put your left hand on her head as you push her onto your dick just as your 8 week pent up balls deposit their seed into her stomach. After a few moments she removes herself from you as you catch your breath you smile look at her sister then utter you can cum. At the last syllable her sister erupts into a series of loud moans as you see her panties get soaked with her juces.