Hi, I'm sorry the late response.
I apologize you're going through that with your brother. He definitely seemed to be taking much of the attention & adoration.
I think the best thing you can do is that for you and your siblings come together and speak to your parents.
First brain dump, meaning that you pour in writing everything you have in mind. You and your siblings, and then refine it. Count how much time was given to him in comparison to you all.
With one person it is less persuasive but with all of you together, it sends a powerful impression.