I highly doubt the senior ladies of the BRF are getting a % of the profits from what they wore to events in exchange for free clothes/use, that gets into very murky waters.
I remember Zara released a jewellery collection with *checks internet* Cajella as well as being a brand ambassador for Musto, Rolex etc but that's all official and obviously she's technically a private person.
Extended family members like Lady Amelia have also released collections and collaborations with various designers but again they're private people who aren't on official engagements.
I suspect that's the sort of thing Harry and Meghan wanted to do with their initial "half in half out" proposal, be luxury brand ambassadors whilst on an official tour and at Trooping etc, which clearly didn't work out in negotiations.
I remember assuming that royal ladies must get a discount or "gift" when they shop but was told "no, the Queen follows a "Caesar's wife must be above reproach" policy. Although I can't find anything official about that.
