I don't see any reason to believe you or anyone else would go to hell just for being transgender. I haven't been able to find any Bible passages that condemn - or even mention - being transgender. Even if being transgender somehow is a sin (though I see no reason to believe it is), we still are all born sinners. If someone tells you that you are going to hell for your "sin" of being transgender, then, by their logic, they and everyone else are also going to hell as well.
The Bible makes it quite clear that some things are sinful. For example:
"And since they did not see fit to acknowledge God, God gave them up to a debased mind to do what ought not to be done. They were filled with all manner of unrighteousness, evil, covetousness, malice. They are full of envy, murder, strife, deceit, maliciousness. They are gossips, slanderers, haters of God, insolent, haughty, boastful, inventors of evil, disobedient to parents, foolish, faithless, heartless, ruthless. Though they know God's righteous decree that those who practice such things deserve to die, they not only do them but give approval to those who practice them." - Romans 1:28-31 (ESV)
Some Christians may tell you you're going to hell for being trans, but how many of them have never felt envious of anyone or coveted anything? How many have ever acted with malice when they were angry with someone? How many have never gossiped? How many have never been boastful? How many have never disobeyed their parents? How many have never acted foolishly? And here's another good question - how many believe they're going to heaven? Chances are that they all believe they're going to heaven despite having committed most, if not all, of the sins listed here, yet they tell you you're going to hell for something that the Bible doesn't even say is a sin. That is not righteousness. That's hypocrisy. The first few verses of the next chapter reveal this:
"Therefore you have no excuse, O man, every one of you who judges. For in passing judgment on another you condemn yourself, because you, the judge, practice the very same things. We know that the judgment of God rightly falls on those who practice such things. Do you suppose, O man—you who judge those who practice such things and yet do them yourself—that you will escape the judgment of God? Or do you presume on the riches of his kindness and iforbearance and patience, not knowing that God's kindness is meant to lead you to repentance? But because of your hard and impenitent heart you are storing up wrath for yourself on the day of wrath when God's righteous judgment will be revealed." - Romans 2:1-5 (ESV)
Towards the end of the next chapter is a message that's important to remember when you have doubts about whether or not you'll go to heaven despite being a sinner.
"For all have sinned and fall short of the glory of God, and are justified by his grace as a gift, through the redemption that is in Christ Jesus, whom God put forward as a propitiation by his blood, to be received by faith. This was to show God's righteousness, because in his divine forbearance he had passed over former sins. It was to show his righteousness at the present time, so that he might be just and the justifier of the one who has faith in Jesus. Then what becomes of our boasting? It is excluded. By what kind of law? By a law of works? No, but by the law of faith. For we hold that one is justified by faith apart from works of the law." - Romans 3:23-28 (ESV)
This passage makes it quite clear that, as we are all sinners, we ultimately receive our salvation as a result of our faith, not through living a sinless life (as living a sinless life is impossible for any human).
Perhaps these passages would be good ones to show to your family if they're acting judgmental toward you.
