Hi CLINTIAN
It is quite hard to give you a definitive answer as I do not know your parents circumstances. If no one lives at home with your parents and your father applied for AA and was successful then they may be eligible to claim GPC as they may be eligible for 2 x SDP.
If you father claimed AA and was successful then it may affect their benefits in a positive way, I would advise you to seek help from your local Welfare Rights Organisation about what benefits they maybe able to claim, Age UK are also very good at helping pensioners claim AA.
Gary
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
