All families are different and will react differently to someone coming out. Attempting to gauge their general level of acceptance might be a good place to start - referencing a news article, or mentioning a film that relates to trans or non-binary issues may help you to understand how willing they would be to accept you. As with coming out to friends, there are multiple ways to have this conversation, whether it’s one-on-one with individual members, or in one large group.
Always consider your safety when planning on coming out. If you live with the people you’re coming out to, or you are dependant on them and you think they may react poorly, consider having a back-up plan, such as a place to stay, or a friend who knows your situation. Planning for something like this might seem pessimistic, but it’s always best to be safe.
It may take your family some time to adjust. They may have known you your whole life and that change may be slow. That does not mean you can’t hold them accountable - you deserve respect, and just because someone is related to you doesn’t mean that they can disregard your gender identity.
Remember, family does not just mean those who are biologically related to you. We all have the ability to choose our own families, and those bonds can be just as strong, if not stronger.