I see so much of my family in this post. My older brother died several years ago at age 26 after a decade or so of varying degrees of addiction. Before drugs, he was the absolute sweetest person. He was handsome, smart, funny, athletic, tenderhearted and thoughtful. Addiction killed most of that before it killed him, but during periods where would get sober, we'd get glimpses of that old person for a little while. And then he would have to leave a job my dad found for him because he was so out of it, or would start to go through withdrawal on our living room couch, or would steal money from one of us before a holiday dinner. It's very hard to reconcile the person before drugs and the addict, and it's so hard to know whether you're being too lenient or too harsh. Even when you know that cutting him off is the right thing, it's incredibly hard to do, because you love him and you want to save that kid he used to be.
There comes a point where you can't let the life of someone else ruin your own. It's horrendous that your parents brought your brother to you house when you explicitly told them not to. Your parents are right when they say you can't tell them what to do, but you can set and enforce boundaries. It's unfortunate, but it seems like your brother and your parents come as a package deal. You can't trust them not to disrespect you by bringing him to events where he is not invited, which means that inviting your parents will also mean the risk of your brother showing up. When you don't want him there, don't invite your parents. It sucks and it's unfair to you, but you have to protect yourself.
For a long time, our lives revolved completely around his addiction but no good was coming from it because he wasn't being held accountable. You can yell and scream, but it means nothing when you always give in to him in the end. If I could go back in time, I would do anything to convince my parents that ignoring his problems is the very opposite of help. You're likely never going to convince your parents that he's dangerous, because he's their son and they still see him as their baby. Emphasize that you love him, too, but his addiction scares you. Tell them that you know he's their son, but you're their daughter and you need them respect that his addiction has impacted your entire life since you were 13 years old. You're 25 now and you need for your world to stop revolving around drug dealers, withdrawal and recovery.
We barely speak now, but I still text him or visit every once in a while to let him know I love him, just in case something happens.
That's great. Keep doing that, cheer on his progress and sobriety from a relative distance, and limit your contact with him and with your parents.