I feel a pressure to never talk to my younger brothers about my own problems, because I want to try and give them a model of the mentality and behaviors I wished I had when I was their age.

Hey Ben - perhaps one of the mentality and behaviours you want to model is the willingness to be open about reality and not hide it. They might know you better or differently than the image you think you are projecting. I don't know how much younger they are, and that's a factor, but perhaps you are closer to one or another.

Being disappointed in your grades and feeling guilty is a reality. If this happens to them, they will want to share it with you. Running out of money is a reality. You hope they will problem-solve with you if that happens. Perhaps you can problem-solve with them.

The fact that you have not made a special bond with one or another brother shows that your parents have treated you all equally and can balance the needs of each child. I hope so.

It's just a thought and depends on age and maturity of brothers, of course, but I suspect they would like to be closer to you.

They will have girl problems, maybe one or another is gay. If you open up to them, they might be more likely to share difficulties with you without being afraid of being judged.

As for this statement

But the larger problem is that there's nobody I can bring things like this to. (Except you internet!)

This isn't the internet. this is hubski. You're not yelling into the void. There's no yelling here, and there's no void.

EDIT: I have a brother who is almost five years younger than me. A real break-through for me was when I confided in him about some romantic problems I was having in my 20s. He was incredibly supportive. It really helped.