Hi az
You are correct, unless your son is in receipt of a qualifying benefit then you will loose the SDP but you will keep your IR ESA, when your son moves out then contact ESA and let them know, you should get SDP re-instated.
You will not be forced to apply for UC, if you receive any housing benefit then I would advise you to seek advice from your local Welfare Righs Organisation;
advicelocal.uk Gary
