Following my Mom's dementia diagnosis my siblings received a copy of her will. Mom's "truth" now depends on who she is with at the moment and is easily convinced to do something in complete conflict of her trust and/or last will. I have co-durable power of attorney and co-guardianship with my sister who has only now received a copy of Mom's last will. Mom did not want my sister or brother to have a copy of her will until she passed, knowing they would argue and bager her with her choices. They are now taking things from her home if the items have been bequeathed to someone and they do not agree it should go to that person. My sister has also moved a large amount of money from Mom's bank account to her own. Are these activities just unethical or are they crimes?
How are your siblings going to milk you for every cent being that you are co-guardian and they have not right to the money currently?
I think instead of getting all sorts of advice from friends that you need to sit down and talk with a real lawyer about this.
Do you know any policemen? Have you ever had any dealings with your local police service? I ask, because one solution that occurs to me would be to discuss this situation hypothetically with someone who can give you professional guidance; then to write in formal terms to your sister, copying in the rest of the family, spelling out the implications of what has taken place and what charges would apply. This would be, then, an ultimatum: cease removing property, return what has been stolen, or you turn this over to the police to pursue. Your sister has been taking the p*ss, frankly, because she has believed that you would allow her to get away with it. Warn her now, credibly, that she is wrong.
I'm wondering what your sister would do if you mention to her that your mom may have to go onto Medicaid and the state will scrutinize the Will, bank accts. and other assets. When they determine that she has taken things illegally, her bank accounts could be frozen and the matter given to the state District Attorney's office to handle as a criminal matter.
Should this happen - it would be out of your hands and she'd be in some very serious trouble.