Do I have an obligation to honor my father in law if he was not involved in my husband’s life since early childhood?
Thank you for your question.
In general, the fact that he wasn’t involved in your husband’s life from early childhood doesn’t change the fact that he is still his father. In fact, even in the extreme instance that he gave him up for adoption, that would not automatically exempt that child from according him honor. The reason is because, he is still the cause for his existence in this world, and he is still one of the three partners that brought about his existence.
On the other hand, in general the level of honor that has to be accorded to in laws is similar to the level accorded to other older people, that one should rise slightly when they come into the room, etc. There are opinions that say one should speak to them respectfully, and great them if he hasn’t seen them in a long time.
ש”ך יו”ד ס’ ר”מ ס”ק כ”ב וז”ל “כתב הב”ח דהיינו שסמכו במקצת לכבוד וחייב לכבדו כמו שאר זקנים חשובים”. וכן ע’ ח”א (כלל ס”ז סעי’ כ”ד) וערה”ש (סעי’ מ”ד) וע’ ג”כ מחזה אליהו ח”ב סי’ נ”ו, ומוריה גליון רי”ז עמ’ צ”ד אות י”ד.