Sorry to hear all you and your husband are going through at the moment
@Mafanwy - you must both be exhausted.
When you were trying to contact the hospital, did you leave a message about the insulin dose and what he should be eating with it, or were you just trying to get help with the Libre? Even good surgeries are unlikely to have anyone who knows much about insulin doses so you really need to speak to a Diabetes Specialist Nurse (DSN) at the hospital about his insulin and food. I know it's hard to get hold of anyone in NHS at the moment, but I'd definitely try to get a message to them if you can. If you can't manage to get a DSN to call you back, you could also try asking for a dietician (ideally you want both).
In the meanwhile, I might be tempted to reduce the insulin slightly to try to stop the night-time hypos if it were me, though I don't know enough about Humilin1 to know if that's going to be effective as I have different types of insulin. 14 is a higher level than he really wants to be after food, yes, but 14 mid-morning (especially if it goes down again before lunch) is better in the short term than 3 in the middle of the night.
A bedtime snack might also help to stave off night-time hypos. If he is able to eat fatty foods with his heart condition then something fatty (like a yogurt or a couple of savoury biscuits and cheese) is ideal as it will last longer in his system - but if he isn't supposed to eat fat then just a couple of savoury biscuits would do.
What is he eating for breakfast at the moment? People here might be able to suggest better alternatives to reduce the mid-morning spike. If you've just been told he needs to cut down on sugar he may be eating other carbs which are equally bad (diabetics are effected by all carbohydrates, including bread, cereals, and lots of starchy foods, not just by sugar). Most people's levels do go up in the morning though, it's not just him. And being on insulin, he will need to eat some carbs, it wouldn't be wise to cut them out altogether.
Btw, while hypos in the night are not a good idea, he would not necessarily go into a coma and die if he had one and you were not awake to help him. Our bodies store glucose in the liver, so it's much more likely his body would just release some stored glucose and his level would go back up again and he'd just wake up in the morning with a bit of a headache and be quite hungry the next day (liver wanting to replenish its store). I don't have any alarms and it's happened to me several times, I've even had a couple of nights when I was hypo more or less all night. It's also quite likely that having the hypo would wake him up - that happens to me much more often.
So while you should keep trying to prevent the hypos and should keep treating them as soon as they happen, just in case (because they can be dangerous), do try not to worry too much about the worst case scenario.
Oh - one more thought - is he testing his blood sugar with a meter whenever the Libre says he's hypo? Libre sensors are a bit variable, they're not always that accurate, especially at the low and high ends of the scale. I wouldn't rely on one telling me I was hypo, I'd always test as well.