The lady is just a great body and very flexible, and she's an ace in the anal! Clearly visible is the coverage of the cock entering the anus, the man clearly takes great pleasure. To extend the pleasure longer, he alternates between anal and sucking, so you can last much longer. But not all ladies agree to it, the majority take in the mouth after anal only if anal took place in a condom.
That's the kind of slutty sister every brother would let work his testicles. And this one probably accustomed her to these pranks a long time ago. At least that's what I would have done. She'd have to suck and spread her legs anyway, so why not with her own man? It's about time she got her ass printed, too, so she can date like a grown-up bitch. Or maybe she's still trying to keep her anal virginity for her husband.