There is no special way to address a sympathy card:
Mr. and Mrs. John Doe is what I would write.
If not directing the card specifically to the daughter in this case, usually you would address to "The Family of [deceased]".
Dear Name of person, Your message. Sincerely, with love, Deeply sorry. Your name
Just the same as you would always address a letter to them. The unfortunate passing of someone's father has no effect on their name, even if hyphenated , as that would be the daughter's birth name.
They arent
Yes, you can.
Unfortunately, you could probably get away with it. If a child is born inside marriage, even if it is not the husband's it is assumed it is the husbands. It will carry the husband's name and he will be responsible for all support and shelter of that child. Even if the couple ever divorce.
Agamemnon is wrong that is Helen's husbands brother
If there is anything I can do............ with sympathy then put your name ok
Demeter's husbands have been Zeus, Poseidon, Iasion and Karmanor She was never officially married though. Sadly, only two of her children shared a father. Zeus was the father
If your husband is not the child's father, it might depending on the situation.If your husband is the child's father, then yes.
couple
No it's not. The name of the birth father will always be that of the man who's sperm produced the baby. Nothing and no-one can change that. It is not legally possible to replace the birth father's name on the birth certificate - with that of the mother's current partner !