Amber
The rules surrounding SDP can be quite complicated and are often only resolved by a Decision Maker making a decision, but in (very) general terms, it is only awarded to someone living on their own who has no one receiving Carers Allowance for them.
As your stepson is living with you and your family, he is clearly not living on his own, but it may be that his circumstances will still allow receipt of the premiun, however, you will need to get face to face advice with regard to showing eligibility.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
