If a child is called to the Torah as a Bar Mitzvah, if the father has passed away, and a step father is taking the parental duties, how should the child be called to the torah by name, as ben birthfather or stepfather's name? is it possible to call him up as both to respect both men

Thank you for writing to Jewish Values Online.

I understand your question as one concerning the proper Jewish etiquette to demonstrate respect for these two important men in the life of this young man.

The answer seems to me to be fairly clear. The Hebrew name that was given to the young man at birth is his name – Ploni ben Birthfather is the correct form (though the name of the mother is sometimes added). That would include the patronymic, i.e., the name of the man who fathered him (unless there were very unusual circumstances). This has nothing to do with respecting, or disrespecting the stepfather; it is simply a fact that this name is how that young man is called.

The only exception to this I could imagine would be in the event that the young man at a time of illness wished to adopt an addition to his name (a custom among some Jews, based on a somewhat superstitious view, probably dating to medieval times, that changing one’s name might confuse the angel of death and preserve one’s life), and took the stepfather’s name as a part of his own. In that case, as an example, for a young man named Moses whose birth father was Saul, and whose stepfather was Hayim, it might be that rather than remaining Moshe ben Shaul, which would have been his given name, he might take on the name Moshe Chayim ben Shaul. The patronymic would not change, but he might add the stepfather’s name as part of his own, as a middle name, if you will.  

Otherwise, the given name is the name of the person, and it does not change with events or circumstances.

I hope that this is helpful.