Don’t use pronouns when addressing those gender fluid folk. Call them by their name. Substitute the persons full name everytime a pronoun shows up. It’s cumbersome but at least no one is confused about who you are talking or writing about. By using the full name, it becomes obvious to others, that the person may have gender fluid ideation.
Or use scare quotes.
But I’m trying to think of an example of when, in ordinary conversation, we use gendered pronouns about the person we are speaking to. For example, “you” and “yours” are not gendered. But I wouldn’t use “his”, “hers”, “he”, “she”, “they”, “them”, etc. unless I was speaking to someone about someone else.