My sister has always had a history of taking what she wants. I have everything in my favour legally to protect my mother, but off and on my mother forgets and when my sisters asks she will give her something, a chair, a painting, but then later she says where did that go? She also has a habit of going in and taking things when we are out of town.im going to change the locks and not give her the key, but I want to tell her my plans in advance in a diplomatic manner. Oh by the way my sister has personality disorder so I'm also dealing with serious mental health issues and want to be sensitive to that as well. I'm trying to keep the peace but am tired of my sister taking advantage of my mother.
My older brother routinely helped himself to stuff from Mother & Daddy's. He'd pawn it, or whatever. He believed as "eldest son" he stood to inherit everything. What an idiot. As time passed Mother & dad realized stuff was going missing--and even after we moved them to an apartment in my brother's home, he was still thieving. Mother was competent and allowed it. Guilt drove her to let him take almost anything. We are slowly sorting mother's hoard from the "big house" that has been stored and slowly she is realizing that many more things are missing than originally thought. Brother died 4 years ago, so there's no recourse there....mother did learn from this to label and catalog things she wants to give to people, but I am sure when she dies it will still be a hot mess. She has promised the same piece of furniture to 3 people.
I was the only one who stood up to thieving brother and called him out--but since Mother allowed it (and usually added some cash to the kitty) what good did talking to him do? It was only when I caught him going through MY bedroom dresser looking for a valuable vase (he was going to have it appraised for me, he said) did I get really, really angry and forbade him from coming to my home.
Some people......sigh.
One small extra suggestion: my friend's mother, who had quite a lot of nice china and paintings and small furniture, put labels on their backs/undersides with the names of the people she wanted to have them.
I wish I could say it successfully avoided all family arguments after her death, sigh... It didn't, but only because of perceived slights about mother's wishes, not because it wasn't clear what those wishes were.
You can't necessarily win :(