If I was a landlord, would I lick my housekeeper and fuck her without a condom? I think no, I would fuck her hard enough in the front and in the anus, and periodically I would call her into my office for gentle and unhurried blowjobs! And gentle fucking and licking? You have to admit it's too much!
Happy sisters can make their adopted brother happy too. And all you have to do is scrub his back. And the fact that he got horny and put it in both of them is just a nice bonus. It's an honor for a brother to cum in the open mouths of his lustful sisters.