If she talks about others to you, then she talks about you to others.

Fact of life.

Silly rabbit

You can't choose your family and just because you're related,doesn't mean you should trust them.I told my brother something very personal and asked them not to tell anyone but he did and as the saying goes " People will reveal their true selves eventually".I love my brother but sad to say,I can't trust him.Your spidey senses about your sister are probably right.

They can be family, co-workers, neighbors. Be careful about sharing information. Be kind to all, trust very few.

I read up on this grey stone " Rock " business in dealing with scumbags.
Horrible Advice !!!!!
I will never let anyone dictate my bloody life, change me because of you.
I have one for you, it's called.
STEAMROLLING
Flat as a pancake.
Should do the trick.

What do you suggest about neighbours that use your information, handle your personal belongings without permission? You never divulged anything to them directly but the bored sadistic old f*s used "it" anyways. It's impossible to do grey rock when they have no boundaries and listen/watch everything you and others do, other than living in total silence, moving, (things no one should have to do) any other options?

Neighbors can be very challenging to deal with. In many cases, they are bored, lonely, have anger issues, you name it. Don't leave any of your belongings outdoors. None. Nothing that they have the opportunity to touch or move around. I wouldn't have any conversations outdoors, including phone conversations. If you must converse outdoors, run a loud white noise machine to mask the sound of your voice. If you like to sit out on a deck or patio, put up privacy screens and plants to shield you from them. Try to avoid interacting with them. Polite nods or waves are fine. Beyond that, no. It opens up the door to conversation, and possible conflict. There are many nosy neighbors out there, and the pandemic has only made it worse. These lonely or angry or bored people have only grown more so. Not judging, just saying. But that doesn't mean you have to interact with them or let them be a part of your life. Good luck.

Yes to all of that especially the anger issues. I've tried most of those things to prevent any conflict and many more. Never tried to have any relationship with them other than fulfilling strata requirements. Noise machines have helped the most to keep their nosy prying ears out. The personal belongings weren't left by me but they still had access to it. The only time I talked to them outside was when they tried to force a conversation with me but thankfully I was able to use social distancing as an excuse. Yes grey rock seems like the best, albeit not perfect, solution for maintaining boundaries with people who can't be trusted, familial and otherwise. I guess you can't control what people will do at the end of the day. Hopefully they decide to get a life. I thank you for your suggestions. May it help
the OP and anyone else going through similar unfortunate experiences.