Mother (84) with npd, bpd, adhd, add, and dementia is utilizing flying monkeys to destroy my life. What can I do about this?

How is she destroying your life?

What business decisions is she making with a dementia diagnosis?

If Mom has Dementia then the lawyer should not be making any changes. She is incapable of making informed decisions and I would call him/het and tell him/her that.

If its inheritance you are worried about whats more important that or your mental health. I would cut all ties at this point. Tell everyone your going incognito for a while. Block every one. You are not going to win this one.

Interesting information regarding the siblings:

https://www.identifyandheal.co.uk/adult-scapegoat-daughter/

"Siblings are an integral part of narcissistic supply for the narcissistic mother. The Adult Scapegoat Daughter due to her position of vulnerability and powerlessness as a child, becomes the target for her siblings and mothers psychological cohesion into adulthood. All of the behaviours and emotional distress that we were subjected to by our siblings and mother during childhood, do not just vanish in a puff of smoke as we reach womanhood, unfortunately. Sadly adulthood for the scapegoated daughter in a narcissistic family does not change, it in fact becomes worse.

Our siblings will go to great lengths to damage our self-confidence and self-worth, to fortify their own. They are forever imprinted and conditioned by narcissistic mother to try to undermine and compete with us in any way, shape or form that they are able to, and their jealousy and envy of the scapegoat runs deep and it never diminishes. This abuse can present in many forms, both covertly and overtly."

When I was falsely accused by a former Mil, I asked the person telling me the information: "How would she know if we have not been in contact for over two years?".

There is safety in no contact, and living your best life possible.

You might benefit by some counseling to put things in perspective because even though your mother is very ill, she is dangerous to you. A therapist can help you decide if you need your own attorney. Or, if you cannot just walk away , how to save your own life.

You matter, your feelings matter. A person is not the devil, cannot be the devil.

" my siblings/their spouse, and other flying monkeys have gotten her convinced that I am the devil and she is actively ruining my life in every way imaginable."

Then step out of her life and let your siblings do the caregiving.

It really CAN be that simple!

Yes to what BarbBrooklyn suggested. Also, you will need either need to completely detach from them or have granite boundaries for yourself that you uphold. The more you are involved with people the more opportunity there is to blame you for stuff. If you extricate yourself from daily involvement they won't be able to point any fingers at you. So if you are managing or providing anything for your mom on a daily basis, you must bow out of doing any of it. If you are her live-in or in-home caregiver, you must bow out of that completely. If she is controlling his children through money (especially if she dangles the carrot of inheritance), you must become completely independent from her or any other family member and have no expectations. It will be hard at first but extremely liberating in the long run. I wish you great clarity as you examine your participation in all of it, and enduring peace in your heart.

Short answer: You've tried to help, and she won't let you. If you withdraw your help, whatever money/inheritance she has will fall into the hands of these attorneys and non-relatives, but then again, if you keep trying, you might want to go over a balcony yourself.
She has personality disorders and ADD but if she's of sound mind, well that's her decision as to how to "enjoy" her life. Which is, without you. I realize she made it in selfishness, but this gets you off the hook in the future.

Tell her it's her decision, but don't expect to come back to you when she messes it up.

Welcome!

If your mother (or anyone else) is slandering you or interfering with your ability to make a living or lead a peaceful life, you should start by engaging a lawyer to send her a cease and desist letter.