Harry didn't get the grades at school to go to university. He basically 'failed' - a 'D' grade in one subject and a 'B' in the other is hardly the sign of someone who has the brains to go to school. He did have the marks to get into Sandhurst as they do additional tests.
The other five of HM's adult grandchildren all have degrees. William changed from History of Art to Geography while Eugenie did her degree in History of Art and Literature. She has worked at an art gallery since leaving university.
Beatrice has a degree in History and History of Ideas. There are jobs that could use those subjects but she seemed to want to go into business but she didn't study the relevant subjects to go into a degree in that area. So when making her subject selections at school she didn't think about job prospects it seems.
Charles and Edward didn't get into Cambridge on merit so there are questions about their degrees.
Neither Anne nor Andrew had the marks to get into university either.
What would you suggest - insist that the universities take in these royals who don't have the grades required?
If you want "real" work as a scion of a rich family is never a problem. If you dont have the brains like Prince Friso did to´manage your family portfolio, you can at least control it or part of it to have an office and a good salary. There are lots of big companies who'd love to have a (slightly elder) Royal prince as a figurehead without the prince having to do more than dining others.
The problem is that they all, like the Sussexes, want to do something that is not being a figurehead. Eugenie might not earn much (yet) but she is a part of the actively working art scene. Beatrice IMHO learns what she needs to know to manage the inheritance she will have after Andrew (for I think the non-stop claim that Sarah has debts is to let people forget that Andrew got rich organising contacts for payment, just like Sarah peddled him to do for the fake sheikh.)
Yes, I believe Meghan prefers to do "humanitarian work" like she saw Diana doing it - the big gestures for the cameras, the speeches, the big projects with a foreword, introduction or even book/documentary "by HRH the duchess" and that was what Diana had to do outside of the Royal Household, even though she had preferred to do it from inside. We don't know how Diana's life would have gone on after her divorce. Having seen her dying so fast after the finalisation of the divorce and with a lot more trust in Harry (and potential Meghan) Charles might be willing to let Harry and Meghan try that out. We'll see.
And if the cost of security is such a problem, they could reduce it to the public engagements both do (which are pre-announced) and let the others go, hoping for the best. It has thus far worked for other Royals as well.
We don't know enough of how they want to live their life when they are private. how much public events they want to do, how much life in the city (shopping, restaurants etc.) and how much just working or lounging in their home.
We'll see about this as well. But at least I don't believe Harry would accept putting shades on his paternal family. He is a knight, a trained soldier, raised as a gentleman and overall a good guy. And he chose Meghan, so she can't be such a bad egg as well. IMHo, of course.