Help! Need Advice ASAP

My grandfather has what appears to be Dementia in the middle stages. He has been showing signs and digressing over the last 8 years. When he first began showing symptoms I alerted my grandmother (his wife) that he was in need of medical attention; she did nothing.
Now he's gotten so bad that he doesnt eat regularly, forgets where he is, forgets how to get where he's going when he drives, is becoming incontinent, is hyper aggressive and almost violent at times....long story short, he is getting very bad, very quickly. He sometimes has what my grandmother calls spells but really look like either a mini stroke or a grand mal seizure. He will get very bloodshot in the eyes, start shaking all over his body and hum for about 30 seconds, then he comes too and is very angry and lost. I believe this may have been the cause of his recent truck wreck. He drove his truck into a ditch and after he had no recollection of it happening.
Here's my question; What can possibly be done to get this man the medical treatment he so badly needs? He refuses to get checked out and his wife refuses to do anything at all, so is there anything in this world that can help me assist a very sick, very stubborn family member?

Help! Need Advice ASAP