Question about Alzheimer's, please help?

My husband's maternal grandparents both ended up getting Alzheimer's. His grandmother died from it and his grandfather is in the last stages of it. My mother in law keeps talking like she's doomed to get it. She's in her 40's and she's already preparing herself and her family for those fateful days in which her mind begins to deteriorate. Which, in a way, I think is smart. But it got me thinking and it makes me worry for my husband and my children. Is Alzheimer's hereditary? I found it strange that a married couple just happened to both get it and wonder if that heightens their risk. I'd like to know what the chances are of my husband and children having the same problem, is there any way to tell? We're only in our mid 20's, but it's something I'd like to do more research on because I believe a disease this devastating will be hard to prepare for. Can anyone please help? Thank you so much.