As for your mum, tell her gently that if she can't get him to eat, YOU will do it, make some kind excuse. It is hard to convince her and yes it would be devastating for her to lose him. The easiest way is to go slow--mother's wellbeing is more important. She will eventually realise that he is dying, and as hard as this sounds, it is her "journey" or "life experience" she will have to learn to cope with it when it happens, we as children, we can only fix our parents' difficulties to a certain extent.
My father coped very badly when my mother died. He first went into denial and literarily made himself sick---at one point he even thought he was having cancer. He couldn't even walk! He is 75 now. It took him 2 years to recover from the shock of losing my mother. I had a life choice--either stay with him OR go back to finish my PhD. As difficult as it was, I left my dad behind and went back to finish my PhD. Some people were very unkind and criticised me because I did not stay with my father. But-- if I had stayed and postponed my phd or applied for a full suspension, he would have still relied on me to get his tea, do the housework, I would have had to do everything for him. But because I said I had to go, he was forced to slowly get himself back on track. I also managed to finish my phd. Now my father is able to drive again, go out and get his own groceries. We have a cleaner coming in every week as my dad does not do any housework but at least he can make a cup of coffee by himself now. This is my dad's story.
Hang in there
love from churchmouse