If a person gets diagnosed to have type 2 diabetes
RECENTLY, there is some chance- say about 20 % that the person can be cured of diabetes with very very strict lifestyle measures like diet and exercise, reduce weight healthily and his remaining insulin
secreting beta cells start functioning normally and that person can be called 'cured' of diabetes as long as he/ she follows the healthy lifestyle and does not face any major stress
But unfortunately when a person has diabetes since more than a year and he/ she is dependent on medications to reduce blood glucose
then it is unlikely to cure his/ her diabetes but it is certainly something fully controllable with good lifestyle and proper medications to the extent that the person lives all normal life.
The literature you have read about cure is mostly under investigation yet. There has been no 100% curative therapy approved by the FDA for type 2 diabetes.
If you have read anything in alternative medicine, I would warn you from such advertisements as they have not been approved by any authorities and they have not gone through any standard clinical trials to show their universal effects on public.
If your father in law is obese
then there is a way called bariatric surgery
whereby many people have gotten cured of diabetes for many years after the surgery. Please read more about it as an obese patient certainly gets benefitted out of it.
If your father in law has fluctuating sugars and he's thin then unlikely any surgery is going to help him.
Please do not get carried away by any ads but be supportive to him for following all the advices his healthcare team has given him to follow. I hope you understand. Take care.