I'm quite impressed by those sketches to be honest. I think you have a good thing with the expression even if I think either RD or Luna should be more excited (ahegao references if you want ?)
And really, I think if the price is 50$ that I'd be willing to pay for both pose 2 and 3. You see, I will need you to work a lot on the faces, that's a must since htat's where the exctiment comes from. I will add details as you progress with the sketches.
I think pose 3 isn't entirely satisfying however, since RD is completely... out of the frame, is it ipossible to see her a bit more proeminently ? Maybe being penetrated herself in a different way ?