Both types are "hereditary" to some degree, but they are very different diseases tecnically speaking, as type 1 is typically developed due to an autoimmune disorder.
I second WaveRider's opinion.There are too many variables in question here to determine your risks for developing any of the two types. If both parents are type 2 diabetic I would get testet now and again for the years to come. And just go easy with sugary stuff and err on the side of caution.
I am atypical type 2. None of my parents are diabetic.
"Is Diabetis a hereditary disease?"
Diabetes has been known to be hereditary more so with type 2 than type 1. There are a number of heredity factors and environmental conditions that will play into if someone develops diabetes. The latter is obesity, bad nutrition, and lack or no daily exercise.
"Will it come mandatorily to the children/Adults of the diabetic Parents?
This is sort of repeat of your first question. Are you asking if one or both parents have diabetes will their offspring[s] become diabetic? To a large extent yes but at times no. Without knowing your history or having your medical records to review there are too many variables in question.
If in doubt go get tested by a doctor.