Well since you're already lubed up...

"Slut, get on your knees. Whore, lay on your back with your face beneath her pussy and start licking."

Once they got into position, you lined your glistening wet dick up with Lucia's asshole and began pushing forward, eliciting a sharp grunt from Lucia. It took a little time for her back door to adjust, but before long you were able to push in and out fully and pick up speed.

"Mmmm, you both feel so good!" Lucia said as her sister reached up a hand to pinch Lucia's nipple.

You continued picking up pace, giving Lucia's ass a hard slap.

"Ai! Yes, Master!" She encouraged, "Use my ass like a toy! Treat me like a slut!"

You gave her ass another hard slap and then reached up to grab a fist full of hair. Using her hair for leverage, you start pounding her asshole hard as you feel your orgasm coming on.

"OH FUCK OH FUCK OH FUUUCKK!!!" Lucia screamed in ecstasy.

As you felt yourself coming to the climax, you shoved yourself deep inside Lucia's asshole and unloaded jet after jet of cum inside of her. Still holding onto her hair tightly, you emptied your balls into your wife / slut and pulled out leaving her asshole gaping for a bit before it returned to normal.

"Why don't you push some of that out and share with your sister." You said as you released Lucia's hair and firmly patted her ass. Lucia readily complied, pushing a small stream of white from her asshole that flowed down her pussy and onto Rosa's waiting tongue.

Rosa dutifully sucked the cum off of Lucia until Lucia had pushed it all out, and kept it in her mouth. Without needing your prompting, Rosa got out from under her sister, pulled Lucia to her feet, and began lovingly kissing her. Their tongues danced in and out of each other's mouths, mixing their saliva with Lucia's pussy juice and your cum from Lucia's ass. You had to admit, the sight of these two making out unprompted was almost enough to get you immediately hard again.

After a few minutes, the sisters pulled their mascara-streaked faces away from each other and each swallowed whatever cum they had in their mouths.