How to deal / cope with anxiety-induced nightmares?

I don't even know if it's a real thing or if there's anything that I could do to stop it, but I'm reaching out in the hopes that someone might have some advice.

Just to explain the origins of the nightmares:

My mother was killed in a car accident just a little over 18 months ago. I was 16. I was the one who got the phone call from the police (who called me simply because I was the last one to message her) and I was the one who had to tell my father and my brother. I've always had issues with dealing with emotions and as per my usual self, I managed over the course of the next six months to block everything out. The pain, the grief. Everything. It's gotten so bad now that I barely feel anything. I feel emotionally mute to things.

But anyway, that's a bit of a side point. Basically... I was the support system for our family. My brother who - at the time - had moved the US a few months earlier and was still settling in (and struggling to manage without my mom who he was very close to) wasn't coping and was incredibly depressed. I was home alone with my Dad who fell apart completely and sunk into a depression. In terms of the way the family and home operated, I was the adult.

Although I've suffered continuously from depression (which was never treated) for as long as I can remember, I'd never been particularly anxious. But that changed when my Mom died and I think, particularly because of how it had happened. I'm admitting here that I know it's trauma-related (I don't know if trauma is the right word). I became increasingly anxious after she died, constantly getting very panicky every time my Dad went out the house without me and also when my brother hadn't texted me within the course of the day. I had several anxiety attacks - none of which was witnessed by anyone around me. I eventually spoke to someone else in our community who had also lost her Mom at 16 and she told me several tips on how she had coped with anxiety - thankfully those tips helped me deal and prevent the anxiety attacks and I've not had one for ages.

But the anxiety hasn't gone away. I can't answer the phone anymore because I'm so scared about what the caller could be about to tell me. And most of all (and it's only something that has started in the last few months), I'm having nightmares. Nightmares all the time about losing someone I love. I used to have nightmares about people breaking into our house and beating my Dad up or people shooting at me or hurting people I know. In the last three weeks I've had terrifying dreams about my great-aunt (who is in her late seventies) dying (one was even coupled with a replayed version of my mother's death). The one last night (they're always particularly bad on Friday nights and to such an extent, that I've started dreading going to sleep) was about my cats being threatened by this very vicious cat that terrorises them all the time. It might sound stupid, but my cats are my babies. They're everything I have and they mean the world to me. I'm so so so scared about them getting hurt or losing them.

The nightmares aren't going away. It's not like I'm thinking about it even when I fall asleep. It's some sort of sub-conscious fear that keeps coming into my dreams and I hate it. I just want it to stop. At this point, I am just so desperate. It doesn't matter what I do before I fall asleep, they still come and I'm scared that they're getting more frequent.

I'm really sorry for the long post does anyone have any advice that they could give me to make the nightmares stop?