If the stepdaughter is already interested in these pictures and videos, then her pussy is ready to be used for its intended purpose. And the stepfather has more right to her than anyone else. He catches a glimpse of her getting a high from his cock, sucking vigorously and greedily. Twisting her around and putting her upright - the man drives the bolt all the way up to her balls. Such a stepdaughter in the house is a godsend. Let her work hard to strengthen the family.
Well I do not know about the undeveloped ass, in my opinion a man very intensely and without preparation fucks a lady in the ass, and she gets a lot of pleasure out of it! So I think the ass is quite well developed.