Diabetes - HOW DO YOU GET IT [ please read my details ]?

So my mum, dad, nan, aunt all have diabetes, and when my mum and dad had me neither of them had it until they gained weight, my dads OVER WEIGHT by MILES!!! and thats how he caught it im guessing and my mum was a taxi driver and never ate properly that how she got it, and my nan ate SO MUCH SUGARY FOOD when she was a kid she lost all her teeth. that how she got it, and my aunty is also like my dad, my brothers and other uncles and auntys don't have it they are all normal weight does that mean i will develop it? And if so, would going on a diet and weighing 60kgs and eating healthy keep me out of the diabetes zone? xx