Comparing yourself to other people, especially when getting older is a dangerous thing to do in my opinion. Lives turn out so differently and we achieve certain things at such a different moment in our lives. I do recognise the problem though. It sucks and is not always easy to manage. Best thing to do for me is to compare yourself to how you were in the past. Set some goals you want to achieve for yourself and go for that. Self-publishing a novel for example seems like one of those goals. And you achieved that. You have potential, it's just different than your brothers. There's nothing wrong with that.