Hi annam
Welcome to the forum.
You might want to have a look at the following FAQ which explains where everything is;
www.benefitsandwork.co.uk/guides-for-claimants/faq/forum.
Unless he is given an extension, if his PIP claim stops then the disability element will also stop in his HB. If his PIP claim is successful then the disability element will be backdated.
He may want to contact DWP and ask if he will be given an extension, if he is given an extension then get it in writing and show the letter to his local authority.
Gary
