Take her to the master bedroom and fuck her properly.

You take your mother's hand and pull her away from the kitchen, all the way upstairs to the master bedroom where you planned to fuck your mother as you have done consistently for the past 6 months. You two walk down the hall slowly so you don't wake up your sister, who was once more home, but this time it was a whole semester she took off since her college had some construction to go through due to a major accident that involved an explosion from a gas pipe. No one was hurt, but classes were canceled for a large amount of students since their classroom needed to be rebuilt and it would take too long for them to fix it in time for the students to get the proper education with the time left so they sent the students affected away for the summer with the money they paid for tuition being used for next semester instead.

When you get into the room you and Mother quickly remove all of your clothes and lock the door behind you. You lay down on the bed together and mother says, "Oh... Brandon, I will do what I can do best." She then goes down and sucks your dick hard. She is really skilled at sucking dick, but given the sheer amount of practice she has had for the past six months it is no wonder that is the case. Then a few minutes later, you cum in her mouth. You're basking in the afterglow of orgasm when someone knocks on the door. It's must be Valerie, your sister! Your sister is a pro at lockpicking, this you know since she taught you after the few times you accidently locked yourself out of your home. You don't know how it happened, you just remember the embarrassing moments where you had to go and ask your sister to lockpick your door.

You better think fast before she finds out what the two of you are up to!