They ask to use the pool.

Tilly waddles around the fence. "Can we use the pool?"
"Sure," you answer. You hear her legs squish as she gets close. "You sound wet already."
She turns red and sits down at your side. The shirt barely covers her ass as she walks; while sitting her butt is completely bare as the material rides up. You can smell the wetness and see it near the bottom of her cheeks.
"I want to join you. I want to stretch my big ass." Tilly scoops up a wad of cum from your back and applies it to her cheeks and between them. She pulls off her shirt and lays down beside you after you scoot over, but on her back. She watches you look her over, and is pleased by you needing to shift your erection.
"The hugeness doesn't bother you?"
"Look at Aggie, of course it doesn't."
"I was going to start with fisting, you should know."
"Good, no wussy warmups."
Aggie rolls herself onto her boobs and her cock slides under your chair. She slides her hands around your asses and then balls them into fists. She pushes them at your asses. To your surprise, Tilly takes it as easily as you do. Aggie keeps sliding forward.
"I hope you can take length too, Tilly. I'm training for width and length."
"Of...course!" Tilly exclaims with orgasm. Aggie just got to her elbows.
You feel your insides clearing the way for this intruder. You wonder what will happen with the cock. You seem to be able to take the whole arm with ease,
"Good," Aggie says as she pulls out. She goes over to the pool and dips her feet in. "This next part will be easier in the water. Just hop on when ready."
Aggie slide in and soon you see two legs sticking up. You look at Tilly and clamber to your feet and help her up. She waddles to the edge and slides in over a leg. By her expression, it found its mark. You hop in and uncannily the foot slides up your butt. You must have made the same face as Tilly since you see her staring at you. She squirms a little. Her mouth opens wordlessly. As you are lowered you come closer together. You are soon pressing against her belly abd tits while your stiff cock is pushing against her pussy.