You’re getting great advice. I would like to urge you STRONGLY to pay close attention to the sibling. In our family, the two older siblings were diagnosed as teenagers with serious mental illness. I thought our youngest, who was 12 when all this started, was doing fine, but she WASN’T. I did all the “right” things, such as keeping her informed and asking how she was doing. I eventually got her help, but she ended up in the ER with a panic attack at one point.
We have close friends who adopted a pre-teen with serious issues. The three bio kids went through majorf trauma because of him the next few years and harbor a lot of resentment against their parents, who did the best they could. Therapy would helped the kids.
Now when I speak publicly about our family, one of my MAIN points is to get siblings help!! Even if you/they think they don’t need it. It’s critical.