[ Ref. Craig Smith in 17.01.15 MMDigest ]
 [ http://www.mmdigest.com/Attachments/17/01/15/170115_104155_Musical%20Book%20Photos.JPG 

Identifying your posted pictures (from left to right) lead to:

1. Wilhelm I (1797-1888); 1861 König von Preussen; 1871 Deutscher Kaiser

2. Friedrich III (1831-1888); 1888 Deutscher Kaiser (99 days only!)

3. Helmuth Karl Bernhard v. Moltke (1800-1891); preussischer
   Generalfeldmarschall, Chef des Generalstabes
   [Prussian Field Marshal, Chief of Staff]

4. Otto Fürst v. Bismarck (1815-1898); 1867-1871 preussischer
   Ministerpräsident, 1871-1890 deutscher Reichskanzler

The pictures of the women (nice to look at!) however show, almost
certainly, _not_ the matching wives!

These pictures and, accordingly too, the musical book presumably date
from 1871 (date of the enthronement of Kaiser Wilhelm I, Friedrich
(later Friedrich III but at this time heir apparent only) up to 1888
(date of Friedrich III's death).

Historical regards from Germany!

Hans-Martin Meyer-Georges
Freinsheim (Palatinate) Germany

 [ Field Marshal Moltke ("The Great Silent One"), born in 1800,
 [ established the concept of separated armies from which modern
 [ (20th century) German military doctrine emerged.  He died in 1891.
 [ Ref. https://en.wikipedia.org/wiki/Helmuth_von_Moltke_the_Elder 
 [ and https://en.wikipedia.org/wiki/Truppenf%C3%BChrung 
 [ -- Robbie