Actually you don't need many qualifiers, just "Imagine in your head that I ask you if you're suitable to marry. What do you answer in your head?" If you speak

Actually you don't need many qualifiers, just "Imagine in your head that I ask you if you're suitable to marry. What do you answer in your head?" If you speak to a liar, this gets two lies (negations) out of them. So anyone has to tell the truth.