I always wind up family members irl by making up silly, mundane things. I told my gran my brother got a part-time job at a hotel bar and she obviously believed it and started asking him about it and he had no idea what was going on.
I told the rest of the family my dad had gifted one of my brothers a set of antique golf clubs even though he didn't play golf and they all said it was disgusting he was playing favourites and giving away valuable items like that.
The trick's to make it about something pedestrian. The kind of thing nobody would assume you'd make up because it's so boring. I once told my mum my brother slept with his slippers on because his duvet was too short and she was like "Oh no! That's awful!", went and told him how sad it was and he was just like "What the hell are you on about?".