Regarding the BRF being slimmed down under Charles, is there actual proof that other European royal families have downsized, ot is it just perceived this way because of the number of monarchs who have abdicated, shifting the focus to the new nuclear family, while the number of HRHs (or equivalent) in these families still exists.
There is absolutely no proof of this.
In Sweden the royal family is actually expanding. It's a small family to begin with because the King only had sisters, none of whom has succession rights because of their marriages (3 lost their royal status because of unequal marriages, and the fourth converted to Catholicism). However, by making Madeleine's children royals the King has expanded the family instead of allowing it to remain small.
In Norway only those in the direct line of succession and their spouses are styled as HRHs, other family members being HHs. This gives it an appearance of downsizing that isn't accurate - the King's sisters went from being HRHs to HHs upon their marriages, as did his daughter. The only difference between them and Severre Magnus (asides from gender) is that the king decided that rather than lowering Severre Magnus' status upon his marriage he would be an HH from birth. Much like in Sweden, the king only has sisters, not brothers, so the family has long been naturally small. If any decision has been made to restrict future royal titles (i.e. if Severre Magnus' children won't be royals) then really that's just maintaining what has been the status quo in Norway since the dissolution of the union with Sweden - since the reign of Haakon VII, the Norwegian royal family has always been limited to the direct line as Haakon only had one child, and both Olav V and Harald V only had one son.
In Spain there has been a focus on the King and his descendants since the restoration in 1975. An argument could be made that the family has been downsized by removing the King's sisters from the Royal Family, but given as the King's aunts weren't a part of the Royal Family during his father's reigns it could also be considered to be maintaining the status quo.
The children of the younger son of the Queen of Denmark bear the style HH instead of HRH. However, if you go back a couple generations and look at the children of her paternal uncle, Hereditary Prince Knud (who was the heir presumptive until the succession laws were changed), they were also born HHs.
In Belgium the royal family is focused on the King and his children, but the King's parents, siblings, nieces and nephews, and aunts are all still a part of the royal family with HRHs. The King doesn't have any male-line paternal cousins.
There is something that can be considered downsizing in the Netherlands, as the King's nieces and nephews don't have royal titles at all, but... Willem-Alexander is the first monarch of the Netherlands since Wilhelmina to have a brother at all, and the first since William II to have a brother who in turn had children. So again, it's not so much downsizing and taking measures to maintain what has become the status quo.
In Luxembourg there is a large royal family who all bear the style HRH. Children born to the Grand Duke or Hereditary Grand Duke are all "of Luxembourg" while other male-line descendants of Grand Duke Adolphe are "of Nassau" - not a new trend.
In Monaco there has been a history of a smaller royal family that owes its size purely to the family not typically having too many children and many of those children not being sons. The current Prince only has sisters. Rainier III had only one sibling, a sister, and his mother was the only acknowledged child of her father. Her father, Louis II, was the only child of his father, who was the only child of his father... it's been a small family for a long time.
In Liechtenstein, the family is actually huge, as all male-line dynastic descendants of the first Prince of Liechtenstein are actually styled as Prince(ss) of Liechtenstein, and they're all HSH. The focus on the monarch and his family isn't new for a reason.
Now, in Britain, the royal family is probably the largest it's been since the LPs were issued in 1917. You have the monarch, her children, some of her grandchildren, some of her great-grandchildren, and some of her cousins. It's large because George V had a number of sons who in turn had children combined with the family being long lived. This isn't likely to continue to be the trend - none of the Queen's cousins can pass on royal titles to their children, her children are likely done having children and have passed it on as much as they're likely to - to 4 grandchildren, as the Wessexes don't really count. As for those 4 grandchildren, only 1 of them at this time can pass on royal titles, William, and only 1 other one will likely be able to in the future, Harry. The family is very likely to downsize naturally in the coming years as the rate of expansion isn't going to match the rate of contraction.
I can see them being a very competitive pair.
