I came out to my dad recently and despite being out as gay for the last few years and him being very sweet and open and understanding in general, the amount of transphobic stuff that came out of his mouth was astonishing. He just doesn't know what it's like. He doesn't understand that its not a chemical imbalance that can be cured. He doesn't understand that medical transitioning is not something that can just sit on the shelf until the family is ready. He doesn't understand that feminine names are dysphoric and that my old pronouns are dysphoric. He just doesn't understand what that feels like despite my explaining it to him. Mind you none of this was malicious. Just plan and simple ignorance.
Cis people will never know what it feels like, the best we can do is try to educate them on why its not ok to do or say certain things. The best we can hope for is that they will standup for us when we are disrespected and love us despite it all.
My dad continues to want to understand and tries to ask questions but its a painfully slow process. I also don't think he's gone out and done any of the work on his own. I think he has just relied on me for education.
I know this probably isn't very hopeful but it's just been my experience with him. My other family members have been very chill about it and just ask simple questions and don't dive too much into it.