I'm so sorry to hear about your DS2. That must hang over you so much. And I completely sympathise about the mad SS accusations. We had a report that said DD only wears her brother's clothes and underwear and has short hair.
We complained and were reassured that having short hair and wearing hand me downs were not safeguarding concerns. We also pointed out that as the school uniform is black joggers and we had several left over from DS it would be bizarre to buy her new joggers AND SHE HAS HER OWN UNDERWEAR.
We also have told school, post adoption support, social services, the hospital, anyone who would stand still, that we needed help with our mental health but nobody listened. DH has been to a lot of parent support groups and mental health walks and I now have a private counsellor.
With regards to getting children into school, we used to go with the "carry them and hand them to the TA" school of thought but that's not sustainable. If we have somewhere he doesn't want to go we now we wait... and wait... and wait... but also use our anti anxiety techniques. It's taken months but he now understands that there are expectations that need to be done before getting what you want e.g. he's just hung up his washing knowing DH would play Wii with him when he was done. We are often late to his dodgeball club and he sometimes still hides behind me for 10 minutes but he does really well now.
We had a fairly understanding school for his first mainstream and he liked it, but learned that if he kicked people he got to go and see the HT or do colouring. But regular breaks out of the classroom, and somewhere to hide in the room, helped a lot. He did tend to go out and run around a lot and they generally let him when he needed it.
The main difficulty with DS in mainstream was people going on and on at him or trying to take things away from him.