You will have an opportunity to listen to some radio chatter during this mission. You may ignore this. There's only one path leading to your goal, so you shouldn't be worried about anything else. You start off on a staircase. Start moving towards the upper floor (#1). Open a door. You should be able to see some terrorists (at least 2) on the other side of this corridor (#2). Start shooting at them. It would be best to zoom in the view. You might as well use the scope (if you have one...).
Start moving forward. I have to warn you, though. You will be encountering enemy soldiers quite regularly (#1). Remember that you're not rushed by anything. You should be able to reach a bigger room in a few seconds (#2). The Legion bomb has been placed here, so you can't use any grenades. Start off by killing one of the nearest terrorists. He will be hiding by the machine. Once he's gone, storm the place with a little help from the rest of the team.
Step up closer to the bomb itself. Press and hold the 'use' key in order to successfully disable it (#1). You don't have to do anything else with this object. Now you will have to reach the main room of the complex. That's where the hostages are being held. Open the nearby door and start shooting at visible enemy soldiers (#2). The terrorists will be coming from many different directions. You will have to be very careful!!
Once you've taken care of the hostile forces move on to the large room. Bear in mind that enemy soldiers will probably use a couple of smoke grenades (#1). Make sure you've secured the whole area. It would be wise to ask your teammates for help. Once you've eliminated the terrorists use the nearby stairs (on the left and on the right of the main archway) in order to get to the upper floor (#2).
You have to be very careful. The area you're about to enter is guarded by at least two additional terrorists. One of them will be standing by the stairs, the other one (#1) is hiding on your left. Head on to the next corridor. You should be able to see a single terrorist unit (#2). Kill the enemy soldier. You may proceed to the next section (with the whole team).
You will probably notice a small door along the way. Open it. The room will be guarded by one of the terrorists (#1). Kill him. Use the nearby laptop in order to deactivate the metal detector. Keep moving forward. You should be able to reach the archive room in a few seconds. Watch out for a guy who's standing behind one of the shelves (#2). Take care of this problem. Head on to the stairs leading to the upper level.
There is an enemy soldier over here, so you must be very careful (#1). Kill him. Turn around and start moving towards the opposite exit. You will come across a new door. Open it and enter the new room. Kill a single terrorist while you're at it (#2). I'd recommend waiting for the rest of the team to show up. You're going to need their help in the future.
Start running towards the next room. A short cut-scene should appear on your screen (#1). It looks like the hostages are being held in the central room of the Parliament. Stand by one of the windows and start shooting at the visible enemy soldiers (#2). You MUST kill terrorists standing near the hostages! They are the main threat you had to deal with. Once they're gone, kill the rest of them. Don't hit any of the hostages. Otherwise you would have lost the whole mission.
Now you will have to get down to the hostages. The easiest way will require you to move to a second room. There's a small passageway located on your left (#1). I have to warn you, though. You will be encountering additional terrorists along the way (#2). Thankfully, they're not too hard to kill, mostly because you should be able to surprise most of them. I would recommend that you clear out all of the surrounding rooms.
Once you've dealt with the terrorist threat gather your people around you. Use the stairs leading to the board room (#1). That's where the hostages were being held. Before you come any closer MAKE SURE you've reloaded your weapon. I would also suggest that you try and find a suitable cover. Approach one of the hostages (#2). You will be presented with a short cut-scene. It appears that new terrorist groups have appeared nearby. You must defend the hostages from being killed. Get ready!!
Duck behind previously picked cover. Start shooting at the enemy soldiers. I would recommend firing with long bursts. That way you should be able to get rid of the terrorists faster than usual. Most of the soldiers will be coming from the nearby stairs, however you should be concentrated on guys standing by the windows (#1). You shouldn't have too much problem with this part of the mission. Once the terrorists are gone a short cut-scene will appear (#2) and the mission is going to end.