To eliminate a Counter-Terrorist who is escorting hostages (without harming the hostages obviously), it is best to use a flashbang or smoke grenade to disorientate the CT player then finish the CT with your weapons as quickly as possible. This works best against bots. If it is a human player, then the situation would normally favor the player who has a higher skill and better weapons. Basically, use non-explosive grenades whenever possible, and try to aim for the CT's head. Be warned though as the CT will attempt to Dodge your bullets and you may accidentally harm a hostage. If you have a sniper rifle, try to find cover (perfect able away from the CT) and take aim. If none of this is possible, then you may need to resort to ambush or/and a combination of the mentioned tactics.