Hi Darren,
So sorry to hear about your dad. Unfortunately, medical mistakes seem to occur far too often and that makes losing someone even harder to bear. You'll find lots of support here and lots of people who understand what you're going through here. Your mom is lucky to have you to help support her. All you can do is try to support one another.
Talking helps and you'll always find someone who can sympathise here, so do keep posting.
Sending hugs...