Hi
This sounds like a similar story to my mother. She was diagnosed diabetic, did very little about it. I dont think she ever had it properly explained to her and within a few months of her being exhausted and losing weight she was diagnosed with terminal pancreatic cancer. She was given no advice about the diabetes at that point, I think it was just deemed to be part of the cancer rather than something that needed treating. Her blood sugar was never checked or commented on
So I am very sorry for your dad and all your family.
I recommend you get some help and advice from Macmillan.
http://www.macmillan.org.uk/Canceri.../Treatingpancreaticcancer/Supportivecare.aspx
and also
http://www.pancreaticcancer.org.uk/information-and-support/diet-living-with-pancreatic-cancer
My mum just ate what she wanted which depended on what she could tolerate. She had vitamin enriched drinks. Eventually, when she had little appetite, we read somewhere that a glass of sherry would improve things. And it did!
I wish you all well
Cara