Pretty sure it really depends on the individual circumstance. Type 1 diabetes also known as juvenile diabetes is NOT hereditary. There is no conclusive evidence to suggest so, according to the experts online, teachers and many books I have read. But, type 2 diabetes, which is becoming an huge crisis in especially the western world, I think, can be hereditary. What I also think is that lifestyle plays a large role in type 2 diabetes and many families with some or all family members having type 2 diabetes, probably have unhealthy lifestyles, so if there are just (overweight most likely) siblings with type 2 instead of a parent & child, it could be due more to lifestyle than actual genes causing it... So basically to answer your question, in regards to the current diabetes crisis in the western world, I think there is quite a high chance to "ward off" type 2 diabetes even if it exists in the family, because in the western world I think at least half if not most of the cases are because of terrible eating, drinking (soft drink, no water etc) and exercise habits. Type 2 diabetes is a bit of a strange disease at least to me because I think you can have it on many different levels and sometimes you can manage it to the point that it disappears because of a better lifestyle. According to the experts anyway ;) One more thing though, I think it usually depends on the cause of family member's diabetes. If all are, well, overweight and lazy, then thats your answer, if not, then there might be a time bomb inside, but I am pretty sure there are worse medical time bombs to have! Hope I helped!