Any question that relates to your family, race, religion, gender, or age are illegal. The interviewer should know not to ask these questions, but if you get them, you should know how to respond.
You’re not required to answer, and can steer the conversation in a different direction: “I’m not comfortable discussing that topic, but I do have a question about your management structure. Can we discuss that further?”
If they pressure you for an answer, then that company is not somewhere you want to work. If they can’t be honest in the interview process, there are probably more things they handle illegally as well!