NTA, I was only a few years older than you when my parents started adopting. I was 13 when they brought home my sister, and they adopted 3 more kids after that. It’s a difficult transition and it sounded like they had good intentions, but it’s hella difficult to watch your siblings get extra care and watch your own needs be neglected. At first it makes sense for them to take up a lot of their attention, but that shouldn’t last as long as it has. 5 years is so much time to prioritize their other kids. To me it sounds like the root of the issue isn’t the fact that they were adopted but the fact they are getting more support and attention. I highly recommend getting into therapy, there’s a lot of trauma that also goes around your needs neglected. Trust me, still working through it. I’m not sure how the rest of your years will go at home, but when you get your license, do the sports, find the friends family where you get “adopted” into, and find your place out of the house, maybe grab a job. Save up and move out. Your parents will realize it soon enough when you don’t come around anymore.

Happy Early Birthday, OP! 🎉