I had a similar situation in my upbringing. When I was growing up I had several health issues and couldn't participate in sports. Both my parants are / were avid sports fans and my brothers played several different sports. This meant that for most of my life when my parents attended my brothers sports events I either was left with a sitter or at a friends house. Sometimes when I got older I was left home alone. Later I overcame the illness and became bigger than them. Which scared them because they used to beat me up.
Neither of my brothers is very good with money and I always had money in my bank account. Still do. So when my brothers wanted something my parants would buy it for them, but if I needed something I was told to use my own money. This further alienated me. Even to this day my parents still react the same. I should say my mom, my Dad died about a year ago. She has given them a lot of things as inheritance, but when I asked about the things I was promised I was told that either she still needed it. Which I know for a fact she doesnt or that she had given it to either my brother or their kids. Or she sold it. I know in her mind she thinks she treats us all equally. She can't see what is really going on and when I try to point it out she just gets mad at me and ends up giving more things to my brothers. Or buying them something. In her mind she thinks I am being greedy because I already have "extra" and my brothers don't have anything. Which is their own fault. Another reason I think it is still the same because my wife and I were very careful with our money and I am now worth more than my Mom. My brothers on the other hand still spend every dime they get before they get it. They are waiting on me to die so they can take whats mine. I might just give it to charity and leave them nothing, but I am to loyal to my family so they will probably still get it.
One thing I did notice was this. At my parents house and at my inlaws house the pictures of myself and my wife were smaller because that was the size we gave them. My brothers and brothers in law purposely had bigger prints made, but because my wife and I were more frugal we got smaller prints made.
People are imperfect and why they do what they do is sometimes impossible to understand. This is where love and forgiveness come into play. I know my parents and my brothers love me and I love them. So who gets what and all that doesnt really matter to me. However I wonder if I was not as financially set if it would matter more? Who knows? Things are as they are. Peace!