As your sisters are still in F/T education they would be able to get advice from their local Connexions service [www.connexions-direct.com 080800 13219], they should have a nominated advisor to provide ANY information they request.
You would probably be best advised to contact your local benefits office[www.dwp.gov.uk] to ask their advice. Other than that try Citizens advice and local Housing dept.
I would still advise talking to your mother and the bloke but if you feel it has already gone too far - get out fast.