Kane Rhodes and Brian Jones are agents with MI-6.
More specifically they are operatives inside the relatively new division with the mysterious sounding name of 'Department X'. That group was "a combination of MI6, MI5 and other British security forces, set up to share information and resources with other secret service agencies throughout the world". As such its members were getting used to spending a lot of time overseas, often working with operatives from other nations. On the surface this would sound like a good idea, and possibly was, since these other agents would often have more knowledge of the terrain and the people. However, it also meant having to trust and rely on people they had never met before and could not say with any confidence were worthy of that trust.
At the start of the first recorded adventure, Rhodes and Jones may have known each other but there is no evidence they had worked as a team before but from their first get-together the camaraderie was evidence as was the assurance they had each other's back.
While neither of these operatives are by any sense old, both likely in their late 20s or very early 30s, Rhodes is the more senior of the two. He has been with the SIS for most of his adult life and has as one of his skillsets being an accomplished sniper.
Jones definitely has had his share of action though that was in the SAS for a couple of tours before making the transition to MI6 two years before.
The two had not worked with, or really knew much about, the other prior to the first recorded adventure but they meshed very well on that mission and would become an impressive team.