Can a man marry his stepdaughter?
Depends on if the man has slept with is wife or not.
If he has slept with his wife?
Then, he can never marry the stepdaughter even after divorce.
What if he has not slept with is wife?
If he divorces his wife without having slept with her, then he can marry her daughter.
What if he only touched and kissed his wife lustfully but did not sleep with her?
According to the Madhhab touching and kissing renders the stepdaughter impermissible.
Can the husband go on Hajj with his stepdaughter as her mahram?
If he has slept with his wife or touched or kissed her lustfully, then he becomes the mahram of his stepdaughter. He can accompany her to Hajj.
Does the Hanafi madhhab consider touching and kissing the wife as having had sex with her?
Yes, it does. According to the Madhhab if a man touches or kisses a woman lustfully, it is as if he had sex with her. The rulings that would come into play after having sex, come into play if he merely touches or kisses lustfully.