Roughhousing with a twist

Zoe squeezes Riley's tits a little more and stick her tongue out at you. "What are you gonna do about it, Jimmy?" You notice, with some dismay, that Riley is staring at you. You have been dedicating more and more time to the weight bench this year. Despite your paunch that won't quite go away, the progress you've made on your shoulders, arms and chest is significant. Now, shirtless, your little angel appears to be on the verge of drooling. This is not good.
Despite this discomfort, you jump into the pool in your khaki shorts. You go commando, so its not that different than swim trunks, really. Your phone and keys are still sitting inside on the dining room table.
Zoe shrieks with delight and fear as you wrestle her away from Riley, playfully. "Dunk time, Little Zoe!" You push her head underwater, holding her only the briefest of moments. This is just fun. Her head pops the surface, and with a big smile she punches your shoulder, tackles you and tries to sweep your legs, but you are bigger and a bit stronger, so you have her in a reverse bear hug in no time. You alternate bobbing her up and down below the surface, until she's spluttering and squirming delightfully. {if Zoe2Plan = 1} This is just payback for the little power play she pulled on you earlier, edging you with her naughty mouth. As you feel her body slide against yours in the water, you remember the feeling of her lips and tongue on your cock, and so does your cock, rising to the occasion. {elseif Zoe3Plan = 1} Your thoughts drift back to making out with her in the office earlier. What was her fiendish little plan? Your cock bounces at attention as you think on her prohibition against sexual release.{else} The close bodily contact with her, even being your sister, has an undeniable effect on your dick. {endif}
"Leave her alone, you bully!" Riley's giggle in your ear is accompanied by a sleeper hold, and her legs wrapping around your midsection from behind. You release Zoe and fall back into the deep end with Riley, laughing. What a fun day this turning out to be.
That's when you feel Riley's hand pop the button on your shorts and slide inside to grab your dick. At this angle, against the side of the pool, there's no way Jenna or Karen can see what's happening.
"You look so good, daddy. I love how much you've been working out..." she closes her fingers around your cock, which isn't far from full mast now. "...oooh...it's bigger than I thought." Her breathy voice is sending confusing signals to your brain and cock.
"Riley...what the....we talked about this..." you are in panic mode. Zoe is climbing out of the pool on the far side, and heading to the outside bar to make a drink. "...besides, what about your mother?! She's going to see this and kill us both, baby." You're frantic, you realize as Riley starts stroking it inside your shorts.
"But...Mom always taught me to share..." her pouty whine is intoxicating. "There's more than enough of you..." she squeezes your cock, "to go around. God...it's bigger than I even pictured...and thick, too." Riley's clearly lost in her daddy fantasy right now. Her desires , plus the ****, are working together to make her so bold as to be frightening.
You're saved as Jenna suddenly plops into the pool on the shallow side. "Oooh that's cold!" Her voice seems to break the spell, as Riley releases your cock, and throws her arms around your shoulders. Nothing to see here, just a father and his daughter playing innocently in the pool.
You swim over to Jenna, with Riley gripping you, and the three of you hug in the center of the pool.
"It's so good to have you home, sweetie." Jenna gives Riley a kiss on the cheek.
"I'm so glad to be home. Momma, you look so good." Riley puts her hands on Jenna's hips. "You're making me so jealous, it's not fair!" her tone is mock tantrum. And her eyes on yours let you know exactly how Jenna is making her jealous. You decide not to interject, instead climbing out of the pool. After that, you need a serious drink. You grab the bottle of scotch from the minibar and pour yourself a short neat. Though it's for sipping, you throw it back like a shot. The burning in your throat is nothing compared to the burning in your balls and chest right now.