I don't think it really shows unhappiness, some are just more comfortable in front of cameras and situations vary. Even QA looked different depending on whether she was posing in England or at home in Denmark. The Prussian WAS a very stiff one. Vicky and "Fritz" had one of the happiest royal marriages ever and a wonderful relationship with their younger children. By this point, I don't know how soured the relations were with Willy, Charly and Henry.
Anyway, geneaologically:
Victoria, Princess Royal of GB m. Frederick III of Germany
1. Wilhelm m. (1) Augusta Victoria of Schleswig-Holstein
(2) Hermine of Reuss
children (all from 1st marriage): Wilhelm (6 children), August Wilhelm (1 child), Oskar (4-5 children), Adalbert (no children), Joachim (1 child), Eitel Fritz (no children), Victoria Louise (5 children, including Queen of Greece)
2. Charlotte m. Bernard of Saxe-Meiningen
1 child: Feodora m. Prince of Reuss (no children)
3. Henry m. Irene of Hesse
3 children: Waldemar (no children), Sigismund (2 children), Henry (died young, no children)
4. Victoria m. (1) Adolf of Schaumburg-Lippe (no children)
(2) Alexander Zubkoff (no children)
5. Sigismund (died young of meningitis, no children)
6. Sophie m. Constantine I of Greece
6 children: George II (no children), Alexander I (one child, Queen of Yugoslavia), Paul I (3 children including Queen Sophia of Spain), Queen Helen of Romania (1 child, King of Romania), Irene , Duchess of Aosta (issue), Katherine, Lady Brandam (issue)
7. Waldemar (died young of diptheria, no children)
8. Margaret m. Frederick of Hesse-Cassel
6 children (incl. 2 sets of twins) Richard, Wolfgang, Christopher (d. WW2, married to sister of Prince Philip, issue), Maximilian (died WW1 no children), Philip (2-3 children), ??. I think 2 died in WW1 and one in WW2?