“I refuse to answer that question.”
None of that is your business. You wanna know if I have responsibilities outside work that might impact workflow, ask exactly about that. If I have a gig on a day and need to take the day off, I'll put in my unpaid leave/PTO/whatever. If I do get married, maybe I'll send you an invite (big maybe).
But none of it, not a single bit is of any relevance to you or your company unless I make it so.
Next day, HR told me my application wasn't going to the next step. I get it if I didn't make the cut in terms of experience and skill. That I respect.
That said, I'm audio recording every interview from now on if it's legal to do so. And I'm just gonna tell them it is an illegal question to ask at all, regardless of recording.