Hi learntorun
You do not need to inform DWP who you put on the deeds, if you are changing the mortgage then that is a different matter and I would advise you to seek help from your local Welfare Rights Organisation; you can find your local Welfare Rights Organisation to help you with advice by clicking on the link below and putting in your post code, it will then come up with a MAP with a list of agencies.
advicelocal.uk Gary