How do we get my husband's uncle to go to the doctor to check if he has a form of dementia?

My husband and I are extremely worried about his 70 year old uncle, as we think he may have dementia. Out of the blue he has accused my husband of having a key to his cottage and stealing his mother's will ( she has been dead about 50 years) that was 2 months ago, and my husband was able to calm him down and he forgot about it. Now he is accusing my husband of breaking into his house and stealing the deeds to land and giving them to a man who we would only know to say hello to. He is a very quiet farmer who has lived a solitary, primative existence, with next to no modern conveniences. We built a house beside him 2 years ago and have been bringing him over for dinner every evening. We are at the end of our tether about this and dont know what to do, he seems fit and healthy in every other way. We know that he has never been to a doctor in his life, so the chances of him having a G.P. are slim, and there is no way we will be able to get him to a doctor. Any advice please? Many thanks