Their mom walked in

Sarah was getting emboldened by the power she felt dominating her brother so easily. She felt a rush of power and desire well up from within her as her massive pale futa dick began to throb dangerously and pulse violently as it slapped against her older half-brothers weak and inferior bitch clit making him whimper with every slap of her meat against his own. Her cock pulsed and throbbed smacking his tiny member again and again with meaty whacks of flesh striking its other part as she ground her cock against his own, growling in dominance as she continued to grind her cock onto him! The feeling of having his small dick beneath her cock was more than enough to make her leak thick globes of precum all over his tiny weak bulge as she leaned down and growled into his ear.
"You are going to love it when I take this thick, throbbing, futa cock and put it so far in your boi pussy that you will learn what it means t be knocked up-"
"Kids! Dinner!" Summer walked to the room all smiles before pausing, looking at her daughter and adopted son on the bed her futa cock grinding onto his tiny and weak bitch boi clit as both gave her a look like deer caught in the headlights as she paused blinking owlishly at them as the two stared back before she coughed once.
"Well! It seems that someone is finally tired of not getting her dick wet! I'm so proud of you dear! I always thought that you would not be able to get anyone besides your brother!"
"W-what?! Mom! That's not true! Don't say that I can get any femboy I want!"
"Sure you can."
"D-don't say it like that!"
"Anyway! Dinner is ready! So you two can come down as soon as you like or take your time if you are a bit busy, but seeing as how no one has all their clothes off tell me would either of you like a bit of a motherly advise to show you how it's done? I'll have you know that I am very good at teaching~" She grinned at the two as her daughter gasped.
"M-mom I don't need you to teach me how to fuck my brother!"
"That is not something I ever thought I'd hear sis... really."
"Shut it! If I wanted to I could get anyone! I don't need advise from our mom!"
"Says the one who is still a virgin."