Angela and I were moaning loudly, a mixture of pain and pleasure as Ross and Neil thrust their cocks into our arses over and over again. Neil tightened his grip on my hips as he began to thrust harder and harder. "Go on!" I urged, "Fuck my arse! Fuck it harder!" Beside me, Angela was urging Ross on with equal vehemence.
"I'm going to cum in your arse! I'm going to fill your arse with my cum!" moaned Neil, his cock seemed to swell even more inside me.
Suddenly Ross moaned. "Ooooohhhh FUCK!" he cried as he sank his cock deep into my sisters back passage. Neil's balls slapped against my enflamed labia as he thrust harder still.
Without warning, his cock erupted, sending jet after jet of cum into my bowels. His cock twitched violently within me as he disgorged his load.
Out of the corner of my eye I saw Ross slump backwards. Angela slid off the sofa and lay down beside him, holding him close and kissing him as he recovered from his exertions. They were joined, seconds later by Neil and me as we collapsed, our energies spent, beside them on the floor.
For the remainder of that final week, Angela and I swapped partners as often as we could. Although Ross and Neil had some inkling as to what was going on, unless they noted the presence or absence of a small scar on their partner's left instep, they never knew for sure just which one of us they were fucking. Not that either of them ever complained. All in all, it was the best holiday that Angela and I had ever had. We're already making plans for next summer.