Can I choose to live with my step father instead of my father if my mother dies? How?

Family lawyers know that it is very hard to tie an adolescent down. If you are 15 or older, as a practical matter it is almost impossible to force you to live with someone you do not wish to live with. You could, through your stepfather, petition the court for placement with him even while conceding legal custody to your biological father (if you must, and only if you must). If the two of them can cooperate about you, all the better. While your birth father is your 'natural guardian,' courts are supposed to take into account the best interest of the child. So the lawyer your stepfather retains will have to gather a lot of evidence and present it persuasively.

The custody orders and your bio father's wishes must be understood.