I would say:
Born to Rule Julia Gelardi (Queen Victoria's granddaughters who were on thrones)
Splendour to Revolution by Julia Gelardi (some Romanov grand duchesses)
Hessian Tapestry by David Duff (the Hesse and by Rhine family of Princess Alice)
The Coburgs by Arturo Beeche
Kings of the Hellenes by John van der Kiste (George I and his descendants)
Kings of the Northern Crowns (?? not sure if that's it exactly) by John van der Kiste
Grandfather of Europe by Theo Aronson (Christian IX and his descendants)
Grandmama of Europe by Theo Aronson (Queen Victoria and her descendants)
Queen Victoria's Descendants by Marlene Eilers Koening
The Grand Duchesses and The Grand Dukes Bk 1 & 2 by Art Beeche, et al
Ted Rosvall's photo books on The Oldenburgs, The Unknown Habsburgs are both excellent (if brief) glimpses at those families.
John van der Kiste also did books--George III's Children Queen Victoria's Children, Edward VII's Children and George V's Children.