I'm going to make my brother end his toxic relationship
Why do you think that his relationship should end?
I don't want to see my brother getting hurt
It's understandable that you don't want to see him hurt. Talk to him and explain why you think the relationship is toxic.
I don't think talking to him is going to work.
I do not think that forcing him is going to work either. It is understandable that you are trying to protect your sibling, I just think that you should find a better way to go about it though.