The genetic predisposition for Alzheimer's is passed through the female line so your husbands children will not be at increased genetic risk of the condition, however its possible the diet/lifestyle factors that triggered or brought forward the diagnosis also apply to his children, so although they wont be at increased genetic risk they may suffer the same environmental triggers.
The disease course for Alzheimer's streches back many years (20+) before the symptoms that may give rise to a diagnosis now. So although we can't turn the clock back it may be possible to slow progression and reverse some of the current symptoms.
It's important to recognise that many of the current problems stem from a reduced ability for the Alzheimers brain to process glucose (from sugar/carbohydrates) so reducing refined carbohydrates and eating a LOW CARBOHYDRATE HIGH FAT diet gives Alzheimers patients an alternative fuel (fat) to use.
Here are a couple of papers that help explain the importance of an alternative fuel source for brains that have faulty glucose metabolism.
"Role of Medium Chain Triglycerides (Axona(R)) in the Treatment of Mild to Moderate Alzheimer's Disease". You can also find Medium Chain Triglycerides in Coconut Oil and Butter.
and
"Ketone body therapy: from the ketogenic diet to the oral administration of ketone ester."
We should also be aware that
"Vitamin D, Curcumin May Help Clear Amyloid Plaques Found In Alzheimer's Disease"
Lifestyle changes have also been shown to reverse disease progression including all of the following were appropriate.
eliminating all simple carbohydrates, gluten and processed food from diet, and eating more vegetables, fruits and non-farmed fish
meditating twice a day and beginning yoga to reduce stress
sleeping seven to eight hours per night, up from four to five
taking melatonin, methylcobalamin, vitamin D3, fish oil and coenzyme Q10 each day
optimizing oral hygiene using an electric flosser and electric toothbrush
reinstating hormone replacement therapy, which had previously been discontinued
fasting for a minimum of 12 hours between dinner and breakfast, and for a minimum of three hours between dinner and bedtime
exercising for a minimum of 30 minutes, four to six days per week