as an addition: the next morning, aunt wakes up, naked. Parts of her body are covered with dried cum (even though she doesn't know that it is cum) She can't remember what happened last night. Cousin (her daughter) tells her, that she helped her to get undressed, so that she wouldn't ruin her dress while sleeping in it. And the dried stuff on her body is probably some alcoholic stuff, because she had some drinks even after she was undressed.
This could be even made into a flashback story. At the start, aunt wakes up like I just described. And then, cousin thinks about what happened the night before - how they undressed her, how they touched her body - maybe the guy even pushed his dick into her mouth (but I think you can call this "oral rape"). Also, the cousin licked the pussy of her mom. And finally, cousin gave him a blowjob, but she told him to shoot his load over aunts big boobs. Swallowing cum is no problem for her, but this time, she wanted to lick it off her moms big boobs ...
And to continue: the family reunion could go for an entire weekend. So they spent another night.
The guy and his cousin want to repeat the last night with aunt. And like before, aunt has some drinks, so aunt, cousin and the guy end up in the same bed again. They want to wait until aunt is sleeping/passed out, so they can have some more fun with her.
But it seems as if aunt didn't drink as much as the day before. She is in a good mood (tipsy), but nowhere near passing out.
A few minutes after the light is turned off, he feels a hand on his dick. But it is strange. He expected that his cousin would grap his dick, but this hand is coming from the wrong (left) side of the bed. Just to make sure, he takes his hands and touches the boobs of the woman on the left. And really - what he feels are the big juggs of his aunt. His cousin has only small boobs. So it is really his aunt who holds his dick. Strange - but it feels good. It seems she knows how to handle a cock.
Suddenly, another hand grabs his cock, this time from the right side. His cousin. She thinks that he is masturbatin, so she whispers "you don't have to masturbate - let me do that for you"
But to her surprise, she hears the loud voice of the aunt: "Hey daughter, take your hand away, I want to play with it right now."
"Oh ladies, don't worry. I am sure I can fuck both of you. And I also have tongue. And I am pretty sure you 2 ladies also can lick each others pussy. That way, everybody would have fun ...
"We have done so much, with so little, for so long, that now we can do almost anything with nothing." - Dave Marcis