Scooped and left alone by PhD advisors. What are my options?
Non-responsive/bad advisors seem to be the rule rather than the exception in acadamia.
Switching programs will probably only result in switching to other bad advisors and cost you enormous amounts of time for little effect on the results. Dropping out because a handful of people aren't as helpful as they once were would be foolish as well.
Finish your PhD and move on.
Lastly: Keep working with mental health professionals. You said you're depressed and seeking treatment. I'm glad you're getting that medical condition checked out. Sometimes that treatment can take time to take effect and get some relief from it. You might also want to interview some other professionals to see if they might have a better diagnosis or treatment plan for you.
These "advisors" of yours are parasitising you, not helping you. Thus, they are not advisors.
Carefully digest this situation, and adjust accordingly. You were deeply affected by the shock of being left alone by the ones you expected help from. But clearly these people are not interested in you, or your career goals. They just want you to either add to their CVs, or else sod off.
As others said in this thread, this is unfortunately common in modern Academia. It is also my opinion that parasitic "bosses" are far more frequent in some institutions and cultures than others.
My main advice is that you focus on yourself, and judge how much freedom of action you actually have. From your description, your advisors are pretending you're invisible, probably expecting you to just disappear. If this is the case I believe this is an invaluable opportunity.
Take as much time as you can in investing in your skills and personal goals, and while trying your best to remain invisible. The most important aspect of your PhD is how you made use of your time, funds, equipment, resources, i.e. not the degree certificate. Your acquired skills, achievements, contacts, knowledge, will move you through your career. Work on those.
I have recently had a similar situation where some postdoc supervisors in China started completely ignoring me as I would not accept 50% payment nor handing off authorships & data for free. I was passive-aggressively left alone helpless in a room, and I can't deal with their language. What did I do? I started working, networking, studying like crazy. I was putting way more effort than any of them, and I acted as if they didn't exist. I have learnt R programming from scratch, and pushed many delayed projects. I have submitted papers of my own, and started exciting collaborations abroad. I have used local structure to do a number of pilot tests on hypotheses of my own, digitalised their most useful & rare references. The pseudo-supervisors surely expected me to freak out and leave. I felt like doing it, but I would just work harder, for myself. They did not stop me. I finished all official procedures with the minimum necessary.
I suggest you do likewise. Good luck!
Yes, all this sounds quite bad and depressing. And I would guess that your advisors might be genuinely let down by that rival publication. But are the things really this bad or is it your perception?
You mentioned a recent loss (my condolences!) and an onsetting depression. Could it be that you see things getting this bad? Slower response times happen in academia (for reasons completely unrelated), less comments may mean you gained on experience and do everything right, so no need for lengthy corrections, etc.
So, one thing of importance is your well-being, so please continue seeing a therapist.
The other crucial question you should ask yourself is: even if all this mishap is not merely a perceived one, how would it hinder you in getting a PhD? You seem to be able to produce research results. Please continue doing so, put them together in a thesis, and defend it. Even if your advisors really "don't like" you, what can they do, if you submit a correct, well-founded, solid thesis for your degree?