Human - you've hit the nail on the head.
Those who provide security for the Royals would have checked out everyone that Prince Andrew was hobnobbing with. It defies belief that his security detail wouldn't have known that he was consorting with a convicted sexual predator.
It also defies belief that his security detail wouldn't have informed him of Epstein's criminal past.
Prince Andrew's security detail has had to deal with his "1000" daliances with women all over the globe that are an open secret. The stuff that gave him the "randy Andy" nickname. So, they are used to looking the other way when he tells them to.
So, it's certainly possible that he told them to look the other way with Epstein and they did as they were told.
However, there must have been briefings with higher level security. PA was traveling, and in fact continues to travel, in the company of very rich men all over the world of all sorts of persuasions. People that have access to confidential information and would certainly like to have access to "influence" as PA is posed. Look at how foolish Sarah Ferguson was duped into a sting by meeting a supposed rich mideastern man who would give her $500,000 for access to Prince Andrew and his connections. She didn't seem the least bit wary. She was used to being around the kind of men Andrew dealt with.
So where did PA's security stay when he stayed in Epstein's Manhattan apartment for 6 days, when he stayed in Epstein's New Mexico ranch, when he stayed in Pedophilie Island, when he yachted with Epstein's topless Thai cruise?
Yeah, Prince Andrew's security must have been reporting to a higher authority
But I think our conjecturing is all for naught. The Royal Family will, indeed, shield Prince Andrew for their own sake. It's despicable, but that's the truth.
It will be ultimately be Charles' problem to deal with his brother. We'll get an idea of what Charles is really made of then. I get the feeling Camilla, for all her transgressions, does not like Andrew.