Hey Rocky. Glad to know that you're trying to get out of the closet. Convincing your family is going to be hard. My parents have seen my thongs too, but they still think that I wear boxers mostly. I'm seeing my parents this summer, and I don't know if I should take some thongs with me. Maybe it's better to stay safe.
I've always kept a pair of briefs in my backpack along with a backup thong, and it's not the first time that I've slipped them on over my thong when I'm near my parents, or relatives. Those couple times my parents actually saw the thongs, they told me to throw them away and such, so I made them think I did, but just kept them hidden ever since, was kind of my fault for leaving them laying around, but honestly didn't know they'd drop by unexpectedly.
Actually, a couple of my younger cousins had unintentionally seen me in a thong before, though this was because they had pantsed me as some joke, they asked what I was wearing, and quickly just made up something and told them that it was related to Gym class, and luckily they bought it and thought nothing of it, lol, dodged another bullet there.