I think all the children of William, as a direct heir to the throne, receive round the clock security.
As far as I’m aware, Andrew pays for his own security. I’m not sure if he still pays for security for his daughters but he did when the rules over who gets security were changed and his daughters lost theirs.
As I understand it, because M+H were full time working royals when they lived here, Harry’s children would have got security. I confess I’m not 100% on that. However, they do not get security as none working royals who actually live abroad. The very suggestion that we should pay for security for an abdicated royal who lives abroad is an anathema to me. I’d prefer a republic, I certainly don’t want my taxes spent on protecting very rich people who do no work for the UK and don’t even live here. That of course is my opinion, unlike the other things I mentioned which are facts.
It’s worth remembering that Louise and her brother James, grandchildren of the Queen, do not get security, and appear to be safe. Why is Archie, a great grandchild, not even a grandchild of the Queen, at more risk than they are. The answer of course, is that he is not. Apart from the fact that he lives in gun ridden America, where 19 children were shot dead just this week. If they are concerned about safety, perhaps the UK would be a safer option.
But it’s their choice, but they shouldn’t expect me to pay for it.