I have a nephew who is similar. Show them the love, I say. Love him, spend time with him, and maybe some sense will rub off. I tell my nephew that I’ll call him by whatever name he wants, but I will not be told what pronouns to use, or else I’m being asked to lie to my own brain and that’s unfair. Calling him by his name of choice is meeting him half way, and hopefully he will see the light someday.