God that's awful, I really wish I knew what to suggest. My Mum's good at things like this, so I'll ask her. Has your Dad got absolutely no records of his own for when (if) he bought the other share. Believe me, I understand how incompetant such organisations are. Southwark has been nothing but a nightmare with my housing benefits, nothing but mistakes made on their behalf, lost paperwork of which I've sent them, having someone else' information in my file including someone else' bank details!, and the list goes on. Agh! is all I can say and that I really sympathise. Don't take any action until you can find a way to make sure.