You’re going to be trapped in the cycle if you don’t get out and you’ll regret it in a few years time. If you can get into a top 20 university then you’re set. People say university doesn’t matter but it does, it also gives you a chance to network.
My advice is, is to just go even if she says no, your brothers are not your responsibility and it’ll motivate them even more to do well if they see you get into a top university. Just regularly keep in contact with them, it’s not the 1900s where people had to write letters, we have devices to contact one and other.