I'm not sure from what you say if he is being tested and is actually having hypos or not? If so, then he needs to test his BG before going to bed and have an appropriate snack if it is not high enough. That's the first thing to try and if it doesn't help, there are other things that could be looked at. What are his BG levels like at different times? What type(s) of insulin is he on and what dosages/when?
A related example is that often when people have undiagnosed sleep apnoea, they cause similar disturbance to their partner and deny it because they are not awake enough to realise what they are doing. If they refuse treatment, about the only solution for the partner is to sleep apart, or somehow record what happens and play it back to them. Another method is for them to have an overnight sleep study, which proves what is happening. It's hard and I really empathise with you.