Mahrams

Do the sons from a previous marriage become mahram to the daughters of the second marriage?

Q: In the Hanafi Madhab, a man has 2 sons and 1 daughter from his previous marriage. He divorces their mother and marries a woman which he then has 2 daughters with.

1. Do the sons from the previous marriage become mahram to the 2 daughters of the 2nd marriage?

2. Do the sons qualify to be mahram to their step mother?