I had to deal with something similar last year when my dad got sick and passed.
First of all, stop with the pity party of “I’m a disabled vet who is being, triggered, bullied, by my hostile sister and it’s giving me a bunch of anxiety and feeling toxic.” Grown men don’t talk like that. She may be the biggest bitch on the planet and trying to screw you over, but its your job to take charge and handle things.
It sounds like the house became property of the trust when your dad passed, and if there is no clause that you’re allowed to live there rent free until you die, you should have started paying fair market value rent at that point, regardless of what he may have told you. This might be the easy solution to staying where you are for the least amount of $.
You’re basically tying up what could be an asset or cash for another investment for her. You could also take your half of the other $ and buy the house, assuming it’s enough $. I don’t know if she could just refuse to sell it to you out of spite, or if it’s even the best decision financially. Why do you need to live in a $650k house in an area with a high cost of living if you’re disabled and don’t work? Go live in a decent $100k trailer in the Ozarks.
When you mention changes being made on the past couple of years, it sounds like she might have tried to get him to amend the trust before he died, possibly under duress or without having a clear state of mind. If she did and you can’t prove he was mentally incapacitated prior to that point, you might be screwed.
It‘s also odd to me, though not impossible, that your son would have been named in his original trust. Generally it’s direct descendants and up to you to give to his grandchildren, etc, unless he wanted you to be skipped but pass it on to his grandson (who would require his own trustee). I suppose if his needs require continued expensive care he might not have wanted it all to come out of your half of the $, but it’s not the norm.
You need an attorney TOMORROW and then likely somebody to interact with your attorney on your behalf.