Hi ckee1999, welcome. Your post stood out to me, and I wanted to make sure you knew you were in the right place.
This is a group that has compassion for your struggles and won't judge you for doing the best you can, no matter whether it looks like "what everyone knows you should do" or not. You know your child, your family, and yourself the best, and you do the best you can with the information you have.
Often, people with personality disorders (pwPD's) believe that something outside themselves will bring them the feelings inside themselves that they want. They have an external locus of control and don't perceive themselves as in control of their lives, choices, and the things that happen to them. For some pwPDs, that can look like "if we just lived in a bigger house" they'd "finally be happy", or if they just had a different romantic partner who was more giving, or... if they had a different body, or body part, or appearance on the outside, they'd finally be "their real self" on the inside.
PD's impact one's very sense of being a self that can make decisions and choices. pwPD's may often have a mindset of "things just happen to me", versus "I can make choices that can put me on a better trajectory".
All that being said doesn't change the agony your family is going through, trying to support someone who is desperately looking for peace coming from external sources. Plus, there's the added level of "ansognosia" (which I'm using in a layman's fashion here, not technical or diagnostic). This really summed it up for me:
rages with constant cries of "I need to die" and "I want to kill myself."
he's 19 and doesn't think he has any issues
That your child can both say "I need to die" and have weapons and a date on the calendar, and (probably almost in the same breath) say "There's nothing wrong with me" speaks to a profound lack of insight that is so challenging to deal with. As I'm sure you're aware, trying to convince someone like that that Yes, there IS something going on... well, it probably doesn't go smoothly.
I also want to comment that I understand how transgender issues can be pretty hot-button. My personal perspective is that there's no "one right way" to deal with a child who identifies as trans, and there can be a lot of "parent shaming" if you're not "doing it" in the mainstream way. As an individual I welcome you to be real, be you, have your own values, and love your child in your own way, even if it "looks wrong" or "people don't agree". Because it has to do with identity, and pwPD's lack a developed sense of individual self, I do have my suspicions that exploring identity in that profound way beyond just "well I'm a goth now" can happen with people who don't understand boundaries, have porous boundaries, lack a defined sense of self, etc. Just my 2cents as an individual.
OK, again, all that being said, you are really in the right place. There are members here who have learned and implemented some new tools and skills for managing these most-challenging relationships. The skills may not be intuitive, but can change the dynamic between you and your child and bring some more peace and space to your family.
That was a lot about me...
Whenever you're ready, feel free to share more about your situation -- I'm curious if your 19 year old targets your daughter? You're right to notice that she feels scared and unsafe, and to think that that's not acceptable.
I also commend you for working to stay together with your husband. A united parental front, and support between you and your H for each other, will be huge in this process. Do either or both of you have a therapist?
Warmest welcome;
kells76