Hi Peter!
Thank you for your message! In these days I made a research and I identified all the officers depicted. A member of another forum suggested me that it is probably related to the Anglo-Egyptian War of 1882 or to the Italian military expedition to Massowa. Both Britain and Italy became involved in the Sudan at that time and there was an agreement between the two Nations. As the British Army was the most experienced of the two in that kind of operations, the officers pictured were probably sent as advisers to the Italian military.