It’s ok for you to feel that way. But also you should recognize that this is the stuff your mom was doing before she got pregnant, and getting pregnant made her feel like she needs to do all this stuff (which she can’t physically do) and more with the new baby, and also added in the hormones which will make her thoughts and emotions more extreme.
So the very first thing you should do here is empathize with your mom about how hard her job is. Maybe if you can’t do more, it’s enough to just recognize how much actually needs to be done and feel grateful someone was doing them before they needed your help.
You sound angry, overworked, and stressed out and that’s understandable. I’m sure it’s not easy taking care of your siblings. But that’s only a fraction of what your mom is feeling like right now. She doesn’t deserve to be insulted. She deserves the help you’re giving her because she raised you right up until now. If she raised shorty children you wouldn’t care about your siblings.
So yeah I think she probably is a good mom who just needs more help. And if you’re doing a lot of work and your mom needs even more help, maybe recruit your brother or half brothers to do some other work. They could do more cleaning or they could hold the baby (12 is old enough to hold or play with the baby for an hour).
I’m sorry if it sounds like I’m just taking your mom’s side, I’m not. You’re doing a lot of great things, and I hope your parents and siblings start to acknowledge that and appreciate you. But I hope you also start to acknowledge and appreciate what your mom was able to do for you all before she had the baby. You both deserve that.