Brother/younger Sister at the kitchen table. Shot in POV for the most part, some 3rd person shots could be in there too.
Sister came back from practice so she's in tight athletic clothing, like volleyball shorts.
Mom makes the two something to eat, and goes up to get a shower before she leaves.
Now here is where I envision it too ways. Either the typical it gets going right away with bro telling sis to crawl under the table because she looks hungry for something else. Or preferred would be bratty sis is just not eating what mom made, doesn't look nearly sweaty enough to have just practiced. So bro connects the dots as he's standing over sis at this point. Weaves his hands through her hair and basically breaks it to her that if she wants where ever she's been going kept a secret...she's gonna have to earn it. She reluctantly pulls his dick out. Right as she starts to suck he pushes her off, she won't get off that easy. So he sits back at the other side of the table and tells her to pop off her top...show them off...and crawl over under the table.
From here sis starts to suck from underneath, even pops up to titfuck a bit from under there. But it's only as sis starts to deepthroat do they hear mom come. Too late to run, and the heavy panting from sis would be a dead give away...so sis has to hold it as mom is grabbing her purse/drink/etc for work and is wondering where her daughter went. Obviously can't tell mom the truth, she's under the table with my dick in her mouth, so bro diffuses it by saying sis went to take a nap or something. Even having to cover up some slight gagging sounds ha. Mom is satisfied with the answer and leaves. Sis pushes off as bro slides back, she's collecting herself now all teary eyed and slobbery. Bro is amazed, encouraging and loving.
The mood changes from a blackmail to sis really getting into it. After she collects herself for a second...bro grabs her hand and pulls her up and bends her over the kitchen table. Rolls down those tight spandex shorts to her thighs and just stick he face in..hopes to give sis a little return favor. Doesn't last long before bro stands up and sticks it in...really rough, but sis is getting into it with dirty talk. Eventually she flips around and rides bro in the chair. Some 3rd person here of her riding, making out, etc. Last part is bro picking her up and throwing her onto the table/counter before a facial finish.
Could see that being an awesome scene with the right performers. Plus the most feasible of the ideas I had (fucking in the park would be tough) for scenes after taking out similar ones that are out there (b/s on christmas morning)