militar

Only one "r" in his last name. en.wikipedia.org/wiki/Charles_Harington_(British_Army_officer,_born_1872) "General Sir Charles Harington Harington, GCB, GBE, DSO (31 May 1872 – 22 October 1940) was a British Army officer most noted for his service during the First World War and the Chanak Crisis." en.wikipedia.org/wiki/Chanak_Crisis "The Chanak Crisis (Turkish: Çanakkale Krizi), also called the Chanak Affair and the Chanak Incident, was a war scare in September 1922 between the United Kingdom and Turkey. Chanak refers to Çanakkale, a city at the Anatolian side of the Dardanelles Strait."

Apparently the saxhorn was "the most common brass instrument in American Civil War bands." en.wikipedia.org/wiki/Saxhorn

memory.loc.gov/ammem/cwmhtml/cwmcap05.html
for details of the various saxhorns.
And a Civil War saxhorn and drum band:

sad how the parents seem to be disconnected to the children. the mother has the baby perched on her lap and her arms folded, and the father almost seems to be leaning away from the young girl.

Some of this , maybe a lot, is informed by the long camera exposures of the day. In most of these photos, the subject assumes a fixed position with the arms usually resting firmly somewhere or otherwise supported. There were also portrait customs which dictated that the subjects of a portrait like this shouldn't be smiling or showing teeth. The father in this one is in a chair, the older daughter on a bench, supported by leaning against him. His head tilt slightly away from her could also be partly due to the saxhorn between them, sticking up over his shoulder. Because of those issues, I don't read a whole lot into this about their relationship.

flickr.com/photos/193005003@N06/52450480476/in/photolist-...

great shot

But what uniform? It looks vaguely British, but - except for the two bars on the right sleeve - there are no indications of rank, corps, or regiment. Wikipedia states that Tanner served in the Red Cross Public Information Department during the war. The uniform could, perhaps, have been a self-designed affair put together by local tailors. However, if he is a member of the Red Cross, the absence of that insignia is puzzling.