You shouldn't blame yourself for being human. Honestly, most people are messed up, in some way shape or form, no one person can handle everything on their shoulders alone. It's okay to feel out of control sometimes, we all do. If you can, try and take some time out every day and let yourself do something that you enjoy, then write out things that you can accomplish the next 24 hours; then do it the next day and so on.
Look, I've been the kid of parents who were letting me down but it wasn't in ways that were financial (at least, that's not what got to me). It was full blown putting me down constantly, being emotionally abusive (physical stopped when I was in the beginning of adolescents) and watching my mom leave for a long time and not knowing if I was ever going to see her again. I don't know your life story and I'm not going to pretend to, but kids are also pretty resilient. I don't know about other family members but I know that as I've gotten older, I'm realizing that there were some areas when my parents were genuinely doing the best they could. Considering they both suffer from severe and untreated mental illnesses; let's just say that it could have been a lot worse.
If you're doing your best, you're not letting your family down. I know you're overwhelmed right now but don't confuse that by thinking you're a failure. You're not. I know because you're still trying and still fighting every single day. You're stronger than you know.