Considering how much they'd been drinking, I'm not surprised they had the idea to have a threesome. Especially since the mom is such a badass. Kissing your daughter in front of her boyfriend meant offering yourself up as a pussy for copulation. And the guy took advantage of that offer by banging both of them. He even shared his sperm with his mother when he came between his girlfriend's legs. Damn, that's fair!
Nice job on his mama by the son. Deep blowjob with drool and snot. Putting his testicles in his mouth. And that lady's ass was a real winner.