The rest should be told from young that they will not be expected to work for the RF.
Peter, Zara, Beatrice and Eugenie already don't work for the RF; they turn up occasionally for special events, but they are not counted as working royals. Louise and James are still in full time education.
I think Harry's problems are
- Too much time on his hands and
- Lack of intellectual resources.
His life before was always structured - school, army, working royal - always planned (largely by other people), always knowing what he would be doing next week, next month or next year.
Now he doesn't have that, he has nothing to take its place. Charles, aside from his working life, has his interest in books, music, art, gardens, nature to fill his time and occupy his mind. Philip had a wide range of interests and no trouble filling his time in retirement.
Harry has none of that. I think he really does need what might be called a 'proper job' - something to give him routine, get him out of the house and give him something to think about other than his own grievances. As a pp said, a ranch or an estate to manage might suit him, but he'd have to be willing to get stuck in and learn the job.