السلام عليكم ورحمة الله وبركاته My father has to wake up at ~05:00 for work. Ishaa is at 23:30 for the whole summer. He often struggles to stay awake and falls asleep before praying. He then does it with his Fajr. Do I tell him to pray Ishaa before sleeping even if it is during Maghrib time?

Well, we have to look into the individual's case. For example, if he slept at 12:00 and woke up at 5:00, and then later on during the day he takes a nap for three hours or so, then this solves the problem. But if the life circumstances are truly not accommodating and he's not able to do that (and we are saying truly that this is the case, not that he just doesn't prefer it), then we say there is no hardship in Islam in the sense where you cannot sleep and cannot work. In such a case, he prays Maghrib with Isha until Allah (SWT) gives him a way out.