contact your local council and get him meals on wheals , the point beiong that its a regular time the guy or woman drops buy with the food and will chat with him for a few mins daily , and not fuss at him for not eating , but these ppl are not daft and if the trays aint empty or touched , or they see it full and in the trash , they do keep a record .Point being hes not bening moaned at to eat , I do understand your worry I really do , My father was the same way .
Your granfather may end up being placed in a hospitail unit where he will be fed desserts and milkshake kinda things with enough to keep him going.
why not even try and bring to the family home for meals , I also diod this with my dad , and it worked for a few years .
but Im sorry to say , you and your family shoulkd contact his doctor and socail servies to help him .
good luck, and my heart feels for you.