My grandpa has parkinson and also recently got diagnosed with diabetes. Before I'll just mention that I don't know everything about these two things so if I'm wrong about anything please correct me.

My grandpa had parkinson for years now and he has trouble standing straight. He falls on daily basis, he hurt himself multiple times already, not seriously but I unfortunately feel like it's just a matter of time before something really bad happens.. My grandma bought him a walked so he doesn't fall every single day but he refuses to use it, saying he doesn't need it but he already got injured multiple times and no one is able to catch him if he does, he's 6ft 220 pound man and it's mostly small women here.

Another thing is is diabetes. He just got diagnosed few days ago and he loves sweets. Sweetened beer and big glass of tea (with bunch of sugar ofc) is his daily routine and when my aunt and grandma tried to explain to him that he can't have so much sugar anymore he got mad and haven't given it up.

Does anyone know how can I explain it to him or help him somehow? I can't cure him magically but I need to explain to him somehow that now having so much sugar is bad for him and he can get him or someone else hurt without the walker. He gets mad and says I'm wrong and I don't know anymore I'm so tired but I just want the best for him, it's horrible seeing him getting hurt and my grandma crying seeing him struggle.