Good morning Sisterstruggle,
My sister is also a drug addict, a lot of people have sent very helpful advice my way if you search for posts that I have started.
I haven't got a lot of time today, but just wanted to say that you come first. If it gets too hard to watch your sister destroy herself, you are under no obligation to stay in contact. And if relatives have a problem with that, you have no obligations to them either.
And don't let her in your house. And encourage your parents to get their valuables into a safe place.
At this time, I have not spoken to anyone in my family for over a month. It went against everything I thought was right, but I must say I have never felt such peace.