They can’t stop him, just expel him from the line of succession and disown him from the family.
That may happen later, but for now it’s a civil lawsuit, so I assume it’s just a matter of money, which, as you pointed out, Andrew has quite a lot of. Even if there later are crimial charges, good luck trying to get him extradited to USA.
Actually, he did have one, in the Royal Navy, for which he receives a 20,000 Pound pension now that he’s retired. Then he was an official Royal going around doing the Royal Family publicity thing, until the Epstein association came to light.
That said, his most recent extravagant purchases were apparently financed by unsecured loans from somewhat shady bankers, who explicitly stated that they did so in order to open further business opportunities with the Royals. This is in addition to unknown sources – no doubt he and other royals and nobility are the owners of some of the impossible-to-identify-the-owners real estate properties, stocks, bonds, and other financial encrustations built up over generations of being in charge.
Other Royal Heirs (he’s 8th in line) have certainly had jobs if not being full-time Royals:
One of them, I note, is a furniture maker, though it is not clear if David Albert Charles Armstrong-Jones gets his hands dirty or just designs the stuff.
From Prince Edward, Earl of Wessex — Google Arts & Culture “…Following a brief stint in the Royal Marines, Edward worked as a theatre production assistant at the Really Useful Theatre Company before assisting in television producing…”
The point still stands - that Royals aren’t barred from working at the threat of expulsion from the line of succession - which by the way, the likelihood of any of her other children sitting on the throne is pretty much non-existent at this point. Charles is alive and in good health, as if William and all three of his children. At this point it’s Charles, William, and George…
Unless Queen Elizabeth just never dies or becomes a mecha or some such…