So, if I'm reading correctly:
You have 2 DS's. One has diagnosed SEN (ADHD & ODD). One does not have diagnosed SEN, but does have an EBD statement.
The school came to the end of their coping strategies 18 months ago, and as a last resort measure, put him on a restricted timetable. You weren't happy, so got legal advice and they were forced to return to full time schooling.
Now, 18 months later, they've got to the end of their coping strategies, despite a statement, and they are looking for a managed move to a Special School.
You are concerned that it will expose him to other children who have similar behaviours as your DS1, who DS2 is mimicing?
Do you think that your DS is simply copying your DS1?
What more do you think his current school can do?
Why don't you think the SS is suitable?
The bottom line is that if his education is incompatible with the efficient education of other children, they can move him.
It's quite unusual to get a statement for a child with no SEN - they are, after all, issued as a Statement of Special Educational Need. Are you sure that he's simply copying his brother - for what purpose?