I'm with stuckinarut:
If some random stranger called you asking questions about whatever private and personal stuff they think of, you would firmly tell them to mind their own business.
Apply the same to nosy elders. They have ZERO authority, and have no justification to start asking questions about your personal relationships.
No need to lie, deny, or imply the other party is lying.
"None of your business what I do or do not do, so please be gone."
If they insist, you could return the favor by inquiring into their personal stuff....like "Have you ever engaged in oral sex? Anal sex? When was the last time you watched pornography?"