Hello from the wife of a lung cancer husband.  Its extremely difficult to be treated so horribly by the one you love but its not your Dad that is doing it, it's the cancer.  I've had a few nasty moments with my husband during treatment but they cope with a lot and always take it out on those nearest and dearest.  Mum needs to walk away when he does this as he doesn't realise he is doing it.  It's so, so hard to have a loved one change in nature but it's not unusual.  Obviously Mum doesn't want this to be her last memories of your Dad and neither do you, so just remember it's not Dad it's the cancer.  Sending my thoughts and prayers to you all.  Carol x