Hello LL, welcome to our community! Your dad sounds just like most type 1 diabetics when they are diagnosed. In you dad's case, his pancreas is probably still producing some insulin. If the pancreas eventually stops producing insulin then he will be diagnosed as a type 1 diabetic. Then he will be given insulin to enable him to avoid high blood sugar and still eat his meals.
Most type 1 diabetics do not have any relatives with type 1. If someone is prone to become type 1 there are many things that can trigger it to appear. When I was 5 I had mumps and chicken pox within a couple of month's time. That weakened my pancreas and soon after that I had all the classic symptoms of type 1. There are many other things that can cause the pancreas to shut down and trigger type 1. I devoted a chapter in the book I wrote to causes of type 1. Type 1 can be diagnosed at any age.
I am not saying he is necessarily type 1, but it seems like that is where he is headed. What are his symptoms? Thirst? Passing a lot of urine? Weak and fatigued? You already told us he has no appetite and he has lost weight. I suggest that he should test his blood sugar at home, if he will. Have him test in the morning before eating anything, and again 2 hours after his first meal. Let us know thIe results.
I have been type 1 since 1945 and I am very healthy. If your dad is diagnosed with type 1 and he takes good care of himself he can have many healthy years ahead of him.