Dear Mark, thank you for your honest answer.
As I know very little about the Indian Army in 14-18, the subject interest me a lot... You gave me a fresh track : I followed it.
I've found the unit on the photo : 15th Ludhiana Sikh Regiment, landed in Marseilles, "acclimatized" in Orléans, then sent to "le Nord" (the North department). The photo was taken in the village of Le Sart, east of Cambrai (spring/summer 1915 ?). Engaged in september 1915 around Ypres, the regiment was later transferred to the Middle East...
The Indian Army, since 1905, had native junior officers, called Viceroy's Commissioned Officers (VCO). Three ranks in the Infantry : Jemadar (2d Lt), Subadar (1st Lt) and Subadar Major (eq. Cpt, 1 per Rgt). They wore 1 to 3 stars on their shoulder straps. They only had authority over the native troops (up to 1917, when Sandhurst took them for training).
I think that the one with the stick is the Subadar Major, the others VCO visible (men without ammo pouches) being his deputies.
Apparently, Sikh NCOs only wore the chevrons on the right sleeve in summer dress (tunic, to confirm).
I also note the closed collar of the European officers... Interesting.