My Question Is About Huntington's Disease. I Have A 76

My question is about Huntington's Disease. I have a 76 year old brother-in-law who has Huntington's in the advanced stage. He has two sisters who are suffering from dementia. The sisters are not always steady on their feet, falling occasionally, but they do not show any jerking movement. I'm wondering if their dementia could be from Huntington's Disease, and is the possibility great enough that I should mention it to other family members who take them to the doctor.
Thank you