3 things about the letter
1: its someone out just spreading rumors to ruin the dad's election
2: someone has "mistaken the step-mom and her lover for the twins" cause face it, the guy looked the spitting image of Shuu.
3: step-mom knew or suggested before hand that if anyhting happened with twins again they should be separated, then she sent the letter.
its all very up in the air at this point ain't it