Mr. Robinson was impressed by how passionately Alex and Melissa had kissed each other. This was turning out to be a very entertaining night.
"OK, you two are about to learn how to use oral sex to give your partner an orgasm. It wouldn't be fair to have you two take turns, since the person who has an orgasm first won't get very much excitement out of stimulating the other one of you. That is why you two are going to pleasure each other simultaneously. Alex is going to lie on his back on the bed. Melissa is going to kneel while straddling his face, and then she is going to bend at the waist and move her head towards Alex's feet while lowering her butt towards his face. This is a variant of the 69 position. What do you think honey?"
Mrs. Robinson was getting wet at the thought of it. She managed to stammer out a reply.
"That's very good. These two had just better remember not to be selfish. It is better to give than to receive, so I had better see these two working hard to pleasure each other, and not just taking in all the pleasure. Alex. Melissa. You two just remember that your only job here is to make each other feel good. Don't get so caught up in your own pleasure that you neglect each other, or I will have your father take his belt to both of you. Now, you two get in position."
Alex eagerly flopped down on the bed, his erect cock eagerly pointing to the ceiling. Melissa climbed up onto the bed on her knees, and awkwardly swiveled her body to place her left knee beside the left side of Alex's face. Her temporarily wide stance rendered her off balance, and she instinctively sought stability. She bent at the waist and let her body weight fall along the natural plane created by her bent knees, and her butt smashed into Alex's face hard. Alex enjoyed the sight of his sister's beautiful buns, but he wasn't expecting them to suddenly clobber him in the face. Melissa immediately lifted her legs out from underneath her, thus putting her full weight on Alex's face. Feeling the cartilage of his nose quickly alerted her to the fact that her brother was under her. She started to gasp in horror, but that quickly turned into a gasp of pleasant surprise when she felt Alex's hands prying apart her buttocks, and his tongue tickling her anus. She giggled with pleasure. An impatient look from her parents let Melissa know that she should probably get into position quickly.
"Sorry Alex, I lost my balance. I hope I didn't hurt your face."
"It's totally OK. You can sit on my face anytime."
Melissa got back on her knees. This gave Alex a great view of everything between her legs. He enjoyed her smooth buttocks, but was even more eager to taste her sweet pussy.
"Wait Melissa. Stay right where you are."