@Stephen I’ve seen that 50% figure before as well, that’s why I asked where you got it from because I’ve never seen any evidence behind it but wondered if you had. Sounds like a good example of never taking advice from a single source, even/especially if it’s from a medical professional 
In absolute terms everyone has 50% chance of getting diabetes – there are only two options, you get it or you don’t. But it’s the likelihood of it happening that you’re talking about.
From the American Diabetes Association stats I make your risk 1 in 17 – so they’re saying that if you have 17 children it’s likely that one of them would get diabetes. Or, if my rusty GCSE maths is right, I make that a 5.8% risk. I read it as, a father with T1 has a slightly higher risk of his children getting T1 than a mother with T1, but both risks are pretty low.
If anyone with a better grasp on statistics than me would like to step in here, you’re very welcome!