I'm upset that my brothers are monopolizing my parents in terms of babysitting
Why does this bother you?
I have to do everything on my own.
It is okay to be upset that your brothers are taking advantage of your parents and leaving you on your own. You should talk to your parents about how you feel so that things become more fair.
I was born first so I should get what I rightfully deserve.
It's fine that you want your parents to spend more time with you, but you have to recognize that your brothers need some of that time as well. As you said, you are the oldest sibling, so your parents are trying to let you be independent. If you really need their help, you can ask for it, but in the meantime, you might enjoy trying things out by yourself.