A very careful look at the slouch hat badge worn in No.1 pic shows it as "ScH"; this definitely indicates Scottish Horse. I have such a (brass) title somewhere and will illustrate it later. As a matter of interest, the SH wore a black, cock's tail hackle behind the hat badge. As shown in your pic. A pity we will never know the names of your three subjects.
Hi again thanks for help so far but still bit confused as the information I have received regarding the photos does not seem to match some other information I have gathered ref regiments etc , here is the information of what I believe to be 2 of my ancestors not sure if all the W Humby details could belong to one person as he seem to transfer a lot,