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.
That's the thing about mature ladies, they don't play hard to get. All their whims are in the past. That's why fucking with them is a pleasure. You said in the ass - they'll be in the ass, you said in the mouth - they'll swallow it with their balls!