Reddit mentions of Hermaphrodeities: The Transgender Spirituality Workbook

This site transchristians.org seems to list common Bible verses and methods of interpretting them to get around their common use as objections to trans people, the sites also got some general stuff on it from a quick flick through (biblical analysis - not my strong point) on various things linking Christianity and trans topics. Have a look through and make sure theres no disasters lurking on the site that will trip you up later.

Reading material may or may not be useful at the time, and may or may not be more useful later while they're digesting the information, or coming to terms with it.

If you want to explore the eunuch/trans angle more you could look into stuff like the Galli (theres more over here The Gallae: Transgender Priests of Ancient Greece, Rome and the Near East - By K. A. Lucker and in Kaldera's Hermaphrodeities) although if you and/or your parents are religious and Christian they may not really mesh well with that information or approach but it indicates that people have been managing to cope with the existence of religious trans people for a hell of a long time.

If you're concerned about rejection from them and are currently dependant on them for housing or finances it may be best to have a trusted friend on speed dial in case you need a sofa to crash on for the night. If you foresee this being a heavy duty and emotional event you may want to make sure you've got a friend on hand for afterwards who can give you a hug, something to eat and generally distract you with company.

Good luck with it, hope it goes smooth and they accept you :)

A pic you might appreciate:

http://odishareporter.in/wp-content/uploads/2017/11/ardhanareswer.png

You might also find Hermaphrodeities: The Transgender Spirituality Workbook to be interesting, along with Transgender Spirituality: Man into Goddess: Sakhi Bhava.